Dont forget how strong aspect of our characters power is their equipment ...
Its huge difference between naked lvl 4 Wizard, and lvl 4 Wizard with best artefacts for his curent build ... even now in EA.
Therefore i dont think level cap at, or just slightly abowe the level we would reach regulary wont be a problem ...
And i mean really slightly, like level 11 in regular game and level 12 for completionist ... wich would also bring slight benefit for Larian, since they wouldnt need to create superstrong spells for final level.

Bcs we can still futher tune, or empower, our character with items.