I mean QoL in more of streamlining how certain aspects of the game plays (some good, some bad). Mainly user interface, the reworking of crafting/gathering, NG+, World Visit improvements, ARR flight, melding etc. In terms of actual content it's lacking compared to Stormblood, but those things are just more conveniences I've been enjoying. The jobs stuff is a whole other discussion, but thankfully those parts do make the experience not feel as clunky as it did previously.
5.3 had the problem of that content coming out but it being spaced so far apart and it wrapped up in about a week. MSQ was long, but like after that you just had SoS on release, which people farmed pretty quickly. Ishgard came after and if you didn't really care about crafting that was basically another empty void of time till Bozja came out. Then when Bozja DID come out most people got their fill just from leveling to max, doing Castrum once, and being done. There's still reasons to go back between farming for the gear, and the Solo fights, but the people who reached that endgame really don't want to bother with that, especially with the queue system for solo fights (which there are posts a plenty about people bitching).
The shelflife of Shadowbringers content really just hit this snag the moment they decided to slide the 2nd ultimate over to 5.5 and cut out the second dungeon for every even patch. If they put it at 5.3 you'd still have people trying things out and the growth for it would still carry over well since even UWU was still actively being run at the end of Stormblood-> Shadowbringers and that came out in 5.3. Then you have the raid tier in 4.4, deep dungeon, Eureka, there was almost always something big coming out each patch cycle that fit the main majority of battle jobs which is what the majority are playing for, that was mainly a timesink (good or bad pending on your pref).
This patch will have a ton of meaty content and will hopefully carry wind over to 5.5, but I think that's really going to depend on the new BA on top of how tricky the raid tier will be. If it turns out to be the same as last where E5-7 can be done fairly quickly and E8S is the long term fight I'm not sure how people will handle it.