I'm paraphrasing/selecting representative samples of your post; I think this is a fair summary?
These things are ~fair criticisms. As others have said, spellcasters are relatively weak at early levels, but get many more spell slots at higher levels (Wizards have ~10 spell slots at level 6, which is more than enough for a single combat). But, being more versatile at later levels doesn't necessarily justify having early levels be un-fun. To this, I reply that low-level spellcasters are at their best when using utility and/or long-lasting spells (buff allies, debuff enemies, escape from melee attackers, mage armor). However, Larian's changes to 5e have made buff/debuff/concentration spells much less useful, turning tactical-utility-spellcasters into inefficient blasters. Particularly the increase to goblin HP has made spells feel less effective even if they hit.
I don't think you get it. It's the system I'm criticising, not the specific number of slots, and as I said, I used the Divinity and Dragon Age franchises because they used systems that were not only different to BG3's but to each other's, demonstrating that there are superior systems one might use. I also linked to the spell list for BG2 which has far more low level spells than BG3 does for some reason. Better to put a cooldown on the spells rather than a limitation on how often they can be cast. Better it takes six turns before I can cast Witch Bolt again than be limited to casting it twice in a fight, as an example. People can accuse me of wanting DOS2 combat but it's not just DOS2, I've never played a game that had such a hard cap on spell casting.
You also have the perfect storm of hit chance being poor, and them not doing a lot of damage when they do hit. A Bow might do less damage than Witch Bolt, for example, but there's no hard limit on how often I can use it, so why would I bring a Wizard over a Rogue? Sure I can revert to Ray of Frost but I can't pin down a target with that, only slow them down and in my experience, Crossbows have superior accuracy for the same damage. Nor can I dip a spell, but I can a weapon thereby enhancing the damage it does. A Rogue is also less squishy than a Mage and because of the idiotic way they've implemented Sleep, a Mage is guaranteed to go out like a light, 100% of the time, when in contrast there are many low level NPC characters that are immune to the same spell. Due to the hard limit placed on spellcasting, there is no upside to having a Wizard in your party.
In short, get rid of the hard cap on the number of times a spell can be cast and replace it with a cooldown. If that means 'DOS3' then so be it. Better a fun game set in the D&D universe than a boring game that's a D&D adherent. At the very least the Wizard class needs to be rebalanced so low level Wizards aren't so underwhelming; and please, can we stop focusing on this single aspect of combat. Combat as a whole, is currently unbalanced to the point of being broken.
