Mostly that i can sort things however i see fit ... that is HUGE plus for me, since i have a little deviation in this matter, i hate autosort and believe that person who maded is should burn in hells. :-/
Also when i do (and if they stay that way

) its much easier, and faster for me to orient in that UI ... personaly i use hotbar in Heroes of Might and Magic aswell, for the spells i use most often ...
And for the third time (is that the expression in english too?) im used for hotbar, many games i play ses them so ... its more friendly for me, than lear to orient in something entirely new with every single game. :-/
There is no doubt a hotbar for most commonly used spells is handy. Most cRPG support that, even with a more traditional UI.
I will contest the last point - if a game uses different system I think it SHOULD use different UI. UI should support game systems, doing otherwise can lead to confusion, rather then learning which brings me to:
Like Heroes of Might and Magic, Dragon Age, Mass Effect, Diablo, Divinity, etc. etc.

Totally not a thing for this kind of games.

That very much underlines the point I made in my previous post. Those are different systems. If all spells would use unified resource, or no resource, it would be less of a problem. Mass Effect/Diablo/HoM&M are different genres all together, with a handful of abilities, and not an entire party to manage. What works for one game type, won't work well for the other. In BG3 what level the skills are, and what action they use is vital - and it requires players to either memorize each spell, spent unnecessary time looking through spell descriptions, or manually organize UI to include those information at the glance. UI needs to highlight those be default, that would be simply good UI design.