I feel like most of the time it's smaller things that bug me most.

For example, if I click the location link on an achievement, let the map stay open and be scrollable. Currently it shows you the spot and, if there's a waypoint there you can use it, but if not you can't scroll around to the nearest one and it just closes the map on you, forcing you to reopen it manually and find the spot again. It seems like such a silly and unnecessary design choice.

The other is builds. If I have a build saved, but I need to swap out a trait or utility for a fight, I wish that change didn't automatically save to the build. It'd be nice if the build only updated when you hit a button to do so.

I do agree, multiple saved cosmetic sets would be amazing. I wonder if they see that as a way they sell gear tabs though.