On skill trees and experience

This really makes no sense to me.

On the one hand you want the skill progression to be meaningful, and on the other hand at lvl 70 I kill 100 mobs and get 15 lvls in the spell progression.

Killing 100 high lvl mobs to get 15 lvls is pointless, it accomplishes nothing but frustration. Zero challenge and just a pain in the ass to respec. Its like saying “Yes, we could make this a QoL but we would rather you kill a few 1 shot mobs so you spend 5-10 minutes to gain 20 levels on a spell you already leveled 100 times already”.

This is just my opinion, but in this way, it would be something that would deter me from trying different builds and characters.

I would make getting 20 lvls WAYYYYYYY harder than it is right now (similar to POE getting lvl 20 gems), and give the option to retain all exp when changing spells when you despecialize (via an in game currency) AND make it possible (via gold or other currency) to remove one point at a time, but make sure if you remove ALL points you still need to prior currency to despecialize the skill from the build.