I'll just get straight to it. Dawntrail will become harder but not just for raiders. It will for casuals and dungeon focus players as well.

FFXIV isn't raising the ceiling however, it's raising the floor. First I want to talk about how this will effect raiders.

Through out endwalker, if you raid savage you will notice a big glaring issue...and that's the overwhelming use of familiar mechanics just repacked in a different way but fundamentally it works the same and solved almost the same. A big one has been what the community calls limit cut.

For the people that don't raid or haven't in awhile. Limit cut is a term we use is when the boss marks the entire party with a number 1-8 and it'll attack each party in that order in a 1-8 set or sometimes by attacking odds first then evens but it's fundamentally the same thing. I can't really remember a lot but I know a lot of savage fights in endwalker had a variant of it. Enough that even yoshida realized the repetitiveness of the use of familiar mechanics.

His words is very apparent that going in Dawntrail we're going to see a lot more brand new mechanics. This technically doesn't make the game harder but at the same time it does because we have to deal with mechanics that are completely brand new, it will be harder not because the game got harder but because we're seeing brand new mechanics we haven't seen before thus not figuring out how to solve/ resolve it as easily. So no more. "Oh this mechanic is just limit cut or this mechanic is just soak towers/share towers" I have no doubt we'll see still stuff like that but I doubt it'll be as common as it was in endwalker savage raids, maybe moved to normal dungeons more often.

Yoshida has also said that they're going to make the enemies target rings smaller. Not this doesn't matter to you if you're a caster but this is great news to people that like to work for their uptime aka melees and tanks. But at the same time this raises the skill floor thus making it more difficult for people that needed this extra help. I need to be selfish and say I welcome this reversion of making the target ring smaller.

This makes melee slightly more difficult in greeding but that was part of the fun imo. So the skill difference between melee and tanks won't drastically increase but we will see a difference in people that greed and people that don't in the dps charts.

There isn't a lot of information but Yoshida really wants to make the game feel more engaging again. Clearly taking in the feedback from the community which is why the hit box Is going to become smaller.

It's clear he wants to raise the skill floor As he said himself that he basically made the game too easy. Not talking about raids, he means everything else. Dungeons, nm trails, 24 man raids and so on. He's cutting the safety net and pushing people out the birds nest so people can fly.

Will this be a good thing overall? We'll see. People forget a lot of non skilled (not a insult..) Are not the best at this game. It's why CBU3 had to add a very easy mode to story mode battles such as in from the cold because people couldn't do it. I know it's hard to believe for people that are good for the game but the game is actually difficult as it is for certain people. I can't tell how much but the fact CBU3 had to add something easier than easy tells you that there is quite a bit.

He's not making the bosses harder but external things that made it easier will be going away as I already stated; Smaller hit box, brand new mechanics and more.

For raiders the game will still feel about the same but the change to seeing new mechanics, smaller hit boxes will make things feel fresh and engaging again but for casual it will feel more difficult if they're not very skilled but I think they'll also like seeing new things from bosses as well, maybe mobs hitting a little harder?

But as yoshida put it. A game without stress is boring.

Now I know this community is full of skeptics and they'll just dismiss everything yoshida said as PR but I don't think saying something is boring as the producer and the director is simple PR speak. I think he means it. But I think it's ok to wait to see yourself if he told the truth or not. Nothing wrong with that. But I believe yoshida and CBU3. They're bringing back more multiplayer and large scale content and most likely longer lived content. I'm glad we have devs that care.

TL;DR :They are not raising the skill ceiling, they are raising the skill floor. Basically meaning they're not going to make things like savage or ex primals harder, they're just going to make things that are overly familiar different such as new mechanics and maybe raise the power of monsters in normal dungeons so they don't hit like a wet noodle. Brand new mechanics doesn't make the game harder but it makes the game feel more fresh, thus making it feel harder because it's things we haven't experienced before. This also along with making bosses hit box smaller increasing the difficulty of keeping uptime as tank and melee dps.