Has the OP played the game in early access?
Setting aside the question of what the ideal level cap ought to be, are you aware of all of the seemingly “simple” issues that were never resolved during early access?
2nd level spells like Darkness have been in early access since the beginning and never been fully implemented correctly. I don’t know if Fog Cloud was ever well implemented. Stealth is still broken. The AI still struggles to deal with enemies that are out of sight. Complaining about not having level 20, when there are still major issues affecting play at lower levels seems weird to me.
I think most people who have played early access will just be grateful if Larian manages do a good job of implementing all spells and abilities up to whatever level cap they set (and ensure that the NPC AI is capable of coping in a decent manner).