Therees a couple of things you have to take into account here i think.
1. Spellcasters seem to scale better so that at higher levels they get immensly more powerfull than meleecharacters.
2. Spellcasters fill other roles than simply doing dammage, they have tons of utility and support that benefit not only themselves .
I can defiantly see where your coming from thou as i often find my priest and mage only casting cantrips or using bows in many fights thus feeling somehow unneeded as my warrios just jump anround slaying everything
But in some encounters they are invaluable and definatly the key to sucess, i am pretty sure the latter will be more prfound when they level up more.
1- that’s very debatable, martialists and half martialists (paladins) tends to fish higher damage against single targets due to extra attacks and feats like GWM and sharpshooter. Yes, AoE/crowd control spells can yield higher DPR when well positioned against multiple targets however their resources get depleted. Think in martial classes as a flat damage per round and casters as descending damage per round through time. That’s in DnD5e. In BG3 the gap is even worst: the ac is lower compared to RAW yet the attribute bonus remained the same. Finesse martialists and high ground archers can deal consistent hits with advantage due to the dumb positioning system while casters can use that system to rely on mostly cantrips which falls off due to the poor scaling.
2-now we’re 100% in accord. I’ve always used casters as an ace that can change the odds of the battle by changing the battlefield. Wall of force, wall of fire, tashas hideous laughter and so on. Even in that field I think the BG3 poorly translated the caster class as we’ll have to think twice before using any concentration spell due to the DOS2 surfaces.
Summing up, it’ll get even worst in full release if Larian decide to follow that lame path. But again, Larian never delivered a balanced game.