Core UI is the same in DQ8 but it's a little more busy because of various additions like more skills, crafting etc. However, it's still pretty simple. Most options are no more than 2 presses deep and usually arranged in the place that makes a lot of sense. Yeah, there's no ability to reorganize skills as you see fit it's automatically grouped by type. Inventory limitations is on purpose so that you don't get access to everything in battle.
Some of those complaints extend to Persona 5 though. You can't reorder skills after you learn them, you can't sort items in the way you want it making it extremely annoying to go through a big list of them looking for the one you want, there are inconsistencies with how some equipment is shown in shop menus, several menus are located in confusing places until you get used to it, etc. There are a ton of problems when you start looking at it.
Then there's the audio-visual component. It's stylish as hell but a bunch of the menus aren't friendly to everyone, particularly the weapon & medicine shop menus which have a ton of colors and movement going on screen when you transition between menus. There's that obnoxious sound when going back in menus too...
Don't get me wrong, I like P5's menus but it's not a paragon of design and what not. There are lots of problems with it just like any other UI.