For myself, this all boils down to a frustration with the Vancian magic system. The limitation is too great or at least *feels* too great. The greatest modern innovation in tabletop rpgs to combat this? Cantrips that you can cast at will.
The ability to cast scalable cantrips doesn't offset this. Balance gets talked about a lot. However, I don't think this is a problem of balance. It's about human psychology. The feel of it. Maybe, mathematically speaking, casters are balanced. But it doesn't matter if they're not enjoyable.
I remember playing pillars of eternity where the Cipher class could cast more spells as he damaged opponents. Mathematically, he would be objectively weaker as he had to roll to hit with a physical attack and then roll to hit with his spells but the freedom of not having limited spells felt great. It's about feeling not maths.