I've seen various comments all over the recent threads about 7★ and how to get STMR but I'd like to expand on some of the benefits they bring, the reason Alim introduced STMRs that is commonly overlooked. As well as explain a bit more on why it shouldn't be as big a concern. It's not just a simple case of power creep.

This ended up really long so it took a while to write. If you want to keep it short there's a series of TLDR and a Super^:p TLDR at bottom.

If you don't know what a STMR (Super Trust Mastery Reward) is, here's a link to the Seven Star Megathread

TL;DR 1: STMR wont ruin the experience as a casual player, only the content they release can. Based on how they've described it and the current state of the game, it's given me the most hope for the future yet.

STMR System theoretically fixes a lot of issues the TMR system introduced into the game. The ability to farm TMRs showed signs of breaking the game from a very early point. Balancing bosses and other content with wide-spread uber-tools was impossible for Alim and for almost a year their trials/bosses have had terrible design since Aigaion. All of this was due to them searching for answers to the current state of things and trying different "solutions" they could come up with. To explain this I'll go over a bit of the reason behind the TMR system.

TL;DR 2: TMRs were a great idea implemented poorly. They were made to reward players pulling multiples of a unit. It also made units with poor stats more desirable, so they didn't have to only release game-breaking units and could introduce power creep slower. Whales get op equips, casuals get better equips, and Alim doesnt need to power creep quickly to make units desirable.

The original purpose of the TMR system back on its release, was to incentivize pulling even if you have the unit already. This is a much better idea than the common method of doing this, stat variation, which they did on their previous title, Brave Frontier. Locking something away solely behind gacha pulls is terrible for casual players so they introduced a farming system to get these rewards for free. I think it may have been for a legal loophole to stall until they could release Trust Moogles, but that's just a hypothesis with little backing. They limited how many you could get this way by making the rate really, really, ^{really, really, really,} really low. Honestly, it shouldn't even have existed because of how abysmal the rate is. It was completely unrealistic to acquire one of these playing casually. General consensus of TMRs in the early days were that they were whale toys. They looked nice and big numbers are cool but you never needed any to clear content. Also by giving units TMRs, they had a value that wasn't tied directly to its stats. That means you could release units that people would still want to pull while not having to increase their stats much, if at all. You could also release lower rarity units with good rewards to compensate players who weren't fortunate enough to pull the main focus unit of the banner. Everybody wins. Whales get op equips, casuals get better equips, and Alim doesnt need to power creep quickly to make units desirable. For a little more on power creep and game direction, /u/Miskatonic_Prof summed it up pretty well in his comment

TL;DR 3: Once content begun to scale around a few TMR. Macroing TMR to catch up to the meta became common. It was "more efficient" than Moogles and significantly less constrained. "Catching up" turned into "why not?" and the rate of TMR acquisition grew uncontrollable. Not just for F2P players but also whales. STMR wont have this problem.

I know a lot of people don't see being able to grab all the TMRs you want as a problem but it really is. It messes with the natural progression of the game. At the start of FFBE, it was apparent that TMRs were just a luxury item. You could happen upon them regularly via dupes (Moogles didnt exist yet) or whale out and grab a ton of a unit. Super Rate Up was an experiment Alim tried to spread TMR a little more. Units were too easy to pull. Players needed 21 of a unit to get a TMR and even with the absurd rates you would need to summon way more than a casual player was expected to. All this did was cut profit margins from whales (bad) and casuals were unable to pull TMR worth of units anyway (bad). They did make pulling specific units for casuals very very easy though and that was awesome. The solution for giving TMRs to casual players were Trust Moogles, a very obvious solution everyone saw coming. After playing for about 3 months worth of content, you would be able to get a TMR for any character you had. No reliance on the gacha for dupes. This was a great addition and gave more incentive to play content. Unfortunately, a portion of the player base had already picked up macros as a solution.

Macros were the players' solution to their lack of TMR while Alim was trying to come up with their own fix. I could go into a whole tirade about how screwed up macros are. That could be another 40K character post entirely with the 2 years of observations to go over there. Love them or hate them, macros were an inevitable development of the farmable TMR system, even if they had nothing but adverse effects on the game. A common belief I read back when macros first became popular was that it was the "only way to catch up to whales". If an F2P can macro their 5★ TMR, a whale can macro all 10 of theirs. There was never any keeping up, only accelerating the baseline expected strength of players. This was not how people were supposed to play the game. They didn't intend to lock the fun of the game behind an inherently non-casual system. That makes the barrier to entry very steep and the game's growth suffers for it. However, you can't go back on things like this in the gacha market or you'll suffer terrible backlash. Playing anti-cheat with every emulator to come out was not worth diverting the resources. So Alim had to just work with what they had. The only way to phase out something broken in gacha games, is with something new.

TL;DR 4: Assuming the release of anything new immediately invalidates the old has always been false. STMR wont make bosses suddenly unbeatable. They wont make TMR useless. They wont make 4★ useless. The only way to remove something broken in gacha games is to release something new.

TMRs were in the game from the start, yet trials that needed TMRs to complete them took at least a year to show up. Lightning, Ramza, Delita, Dark Cecil were all ridiculously strong on release but not needed for content at all. As trials and events grew more difficult, 6★ units became more plentiful. 3★ and 4★ could become formidable 6★ units as well. Alim does make egregious balancing mistakes from time to time, like Ramza, Rikku, Orlandu, Lila. Those are poorly balanced skills, not poorly balanced stats. Broken skills can be on any rarity unit. Because a smaller portion of players will have 7★ units, Alim can build content without taking them into consideration for a while. By controlling the release of STMR Moogles and the UoC tickets. They can keep average power level growth in check a lot easier, and not need to work around a perpetually spiking base power.

Players typically don't like having their units weakened. Firion caused HUGE contention back when a bug making him a one-man army was fixed. Ratings for FFBE plummeted. Even though this was a very fair balance decision, it was immensely unpopular. The idea of not being able to have the most powerful stuff in the game easily may not be popular but its crucial for balance and in the long run makes for more enjoyable gameplay and longer life for the game. Not being able to stack TMR in GL was initially viewed as a terrible idea. Even I thought this at first because I had only known JP's system. By requiring multiple different TMR, players could use more units instead of doubling or tripling down on just one unit. Different TMR with identical effects would still be desirable because you could use them together and significantly slow the power creep of the game. It makes sense in hindsight but at the time it seemed ludicrous. Just goes to show that what we think now may not be accurate to how it all plays out.

TL;DR 5: A lot of initial panic is based on doomsday assumptions. STMR may actually provide a more stable game if done correctly. There's no guarantee it will be but Alim has a decent track record. It's too early to pass judgment.

I'll go into why obtaining a 7★ unit might be easier than expected a little later, but the real big shocker was requiring 6 5★ units to obtain a STMR via gacha. Alone that is very alarming but it was already stated that Super Moogles would be a thing. Back when TMR were released we had no such guarantee, only an assumption and no guarantee. Super Moogles will be the way that casual players can acquire STMR, similar to how Trust Moogles were supposed to be how TMR were gained.

Despite the dupe system put in place to gain a 7★, there are already measures put into place to make 5★ more accessible. The rate of base 5★ units from gacha increased from 1 in 100 to 1 in 33. The odds of pulling the banner 5★ haven't changed but doubled and now you can get random 5★ and dupes a lot more easily. In addition to this, after participating in enough events, players can choose to get a 5★ unit no RNG required. That means if you've pulled ANY 5★ that can be upgraded to 7★ all you need to do is get 10 UoC Tickets and you can upgrade them without relying on gacha.

We aren't currently sure of how frequently we can get these tickets but at the minimum we can assume we can get 2 every Moogle King event. Alim could still give these away in any of their content. Trials, Raids, Story, or Story Events. Either way it provides more incentive to playing the game. Getting a duplicate 5★ isn't that unreasonable.

STL;DR: The current TMR system threw the entire game's balance out of whack. The system was a good idea with a major flaw that STMR addresses. It's too soon to dread this but also too soon to praise it. Let's wait and see.

Edit: Linked to the wrong comment, also the Banner 5★ rate DID double. I got the math wrong there.