Here's the thing. There are certain stacking units that stack up insanely fast if we're talking about 20 turn fights, which means that there are 2 ways to counteract that with difficulty:

1- make the final phases hit for 3m supers and over a million attack stats. - i doubt that's what they'll go with, for multiple reasons: it'll invalidate all non-stacking units in those events(not that it's necessarily a bad thing. I just don't see that happening), it's very easy to mess it up and make the event easy af and, continuing the first reason, it would mean that the new units would either end up being perfect for those events but would get one-shot by today's difficult content, thus getting treated similarly to the buu duo, or they'll end up being broken(and by broken I mean some nigh str super gogeta shit) everywhere. Doesn't seem like they plan on that.

2- make the fights hard from the get go, just have the bosses have either more phases or more hp/damage reduction. This, I can see happen, as it can be clearly seen that the starting phases difficulty jumped in the past year, even without considering the new red zone stages. Teq omega, compared to, well, every difficult event prior(except for red zone cell max), is hitting very hard while making sure one of your units doesn't get to super. The theme seems to be going in the direction that there would be a mix between long/short content, but the starting difficulty is starting to go up.

Now, what does this mean for our beloved build up characters? Well, some of them would probably manage. Some, however, would still have the same problem- they'd die at the start of the fight.

Tldr: longer content wouldn't revive build up characters who are bad in the current meta.

P.S.- I wrote this entire post because someone said you'd be able to bring teq gohan to new events if they were longer. I love teq gohan, I always have, but it's time people accept the fact that his start of turn defense, even with guard, would get him killed by normals. His eza is gonna be monstrous though. AlL hE nEeDs Is MoRe DeFeNsE