Steps of Faith was nerfed because it required a lot of coordination, DF groups were bad at that, and then people started quitting as soon as they got it. That created a wall on the MSQ that players couldn't get through. It's not a situation where newbies can just "git gud" because they don't know what needs doing on the fight, and if the people that do know get it in roulette and immediately bail, how does that work? That one is on everyone who bailed every time they got it rather than try to organize the necessary coordination. That fight had a lot of moving parts pre-nerf and teams needed to know to do the correct things.
Shinryu was also hard, but it wasn't nerfed because the same problem didn't manifest. Generally speaking people stuck it out and tried to help new folks through it. Although it did have wipes and disbands, it didn't have the same kind of huge barrier to the MSQ problem. I saw a lot of stuff from the playerbase on that encoraging other players to stick with it and not bail precisely to try and avoid a nerf, so props to the playerbase on that. Part of the price of harder baseline content is that those of us who know what we're doing are going to need to be prepared to lend a mentoring hand.