I'll be writing mainly about Normal Content here. I know endgame hardcore content has its own separate issues, and I'm not sure if I'm the best person to talk about them. This is my point of view from a player who jumped into the game months ago, and as fresh blood, I think our opinion of the overall experience we have to go through is important.
So, first of all, I'm happy that Endsinger was ilvl synced. It was something that, would seem, most of our online community agreed with, and it happened faster than I expected. That said, I still find it odd and neglectful that the rest of the capstone trials were left untouched when they are even in more need of saving. They fixed the final boss of the latest expansion while, at the same time, they opened the gates to potential new and returning players with the expanded Free Trial, yet they did nothing for Shinryu and Thordan.
That said, it's not only the Capstone Fights which seem to have scaling issues. All through the game so far, the difficulty curve has been one wild rollercoaster that I can't really seem to make sense of. Some bosses are incredibly easy while others are just hitting the sweet spot, and sometimes that happens in the same instance! There are dungeons where some bosses get deleted by anyone with a keyboard, and then the next boss needs you to pay attention to what you're doing and doesn't dies in five seconds. An example during Alliance Raids would be Arachne and Ozma. Arachne, half the time I play, has her second cocoon phase skipped by DPS, whereas Ozma always takes about the same time to kill no matter the group. Or Ultima Prototype and Scathach, with Prototype's HP bar melting fast.
I can also understand why some older raids feel easier during the earlier encounters, but the jump from Cruise Chaser to Alexander Prime, for example, is huge. Cruise Chaser is no harder than any dungeon boss, yet Alexander Prime feels like some of the later Omega bosses in terms of scaling.
I had the luck of getting groups to defeat the Lords in SB and they were amazing fights that didn't end too quick but didn't drag on forever, and yet Suzaku is a longer battle than Seiryu!
Not only I feel we need revisions to older content ilvl sync, since this was supposed to be the "MMO where older content always feels fresh", but also a reason to do it once in a while besides roulette. Faux Hollows is an interesting way of making people engage with older Ex content in the shape of Unreals, but the problem is that the content rotation is incredibly slow and most of the rewards can be acquired through the marketplace. Wondrous Tails is also a good idea, but people would rather Unsync to do any of the activities than queueing/PFing for it.
What I mean is: there is no real use to DF for most of the Normal content besides once-and-done clears, and it would be great if there was a reason to revisit them and help populate them, but that wouldn't be fun unless they also worked on making it engaging again, maybe with just ticking whatever they need to in order to change the ilvl scaling.