"Except while fighting"....yeah. Cool I can pick abilities that would fit my current fighting situation better, all I have to do is reload an older savegame before the fight because I can't do it in the fight where I'd need it. Brilliant. 
I mean...what are we arguing about here? DAO had several huge quick slot bars. You were able to switch through them via UI. How hard would it have been to implement this for DAI? "Made by pc players for pc players", remember?
Well you should be better prepared shouldn't you?

I don't know why this issue is a PC-Player issue, surely console players would experience the same level of distress and heartbreak at such an unnecessary GUI travesty?
Maybe the idea was to make the onscreen display more minimal. If they had put in 22 but left out the minimap, doubtless that would also have been wrong.
Lots of games only have 8 or 9 slots anyway and actually we get a full 8 for spells and whatnot and 2 dedicated potion ones. Some games don't even get that...
Plus, personally, I think it means that you have to plan more and think about what you need, a bit of strategy. Nothing wrong with that...