You're talking about 100 levels that those have to be spread out over. A lot of jobs max out around 24-26 abilities (not counting role actions) that will be set up on hotbars at a given time. if 10 of those are getting learned in level 1-15 and another 10 in levels 16-50, that doesn't leave much to learn over the next 85 levels. Traits don't cut it as being interesting things to learn when all they do is passively enhance a skill we're already using so it just has a flashier animation and slightly increased potency.
That could be a good discussion by itself, but it's really getting off topic for this thread and I don't want to totally derail it.
I think the core of the problem is players expecting action game play in a story driven RPG. Action games will dump you into the big skills almost right away. RPGs have skills slowly build up over time, just as they would in real life. With level sync in dungeons, we're re-experiencing what things were like when we were first starting out and that gives us a greater appreciation for how much our characters have learned since.
There's plenty of content to do if someone wants to be using their max level toolkit whether that's doing max level content or doing lower level content unsynced. The options are there. Switching to a power scaling system would take away that option to re-experience what things were like when we were first starting out.
There are still plenty of players happy to do the roulettes even with level sync. Someone at max level who dislikes level sync doesn't need to think that the poor sprouts are being ignored. Duty Support doesn't exist because fewer players are doing roulettes. Duty Support exists to give options to someone who prefers playing solo or would prefer to learn mechanics before jumping into a group of random strangers, which all too often are harshly judgmental of new players in other MMOs so new players fear the same experience here.