One thing to note is that we don't have many of the powerhouse spells yet-I suspect the game would be exponentially easier for a blaster wizard with a good fireball, simply because you could slam one into some of these high enemy encounters and start really knocking enemies down. Some other key spells are 3rd level as well-hypnotic pattern, for instance. Yes, they are save based, and Larian very favorably interprets advantage from height and backstab, but I'm kinduve okay with that? It's okay that attack rolls are better than normal, casters would otherwise completely dominate the game.
The HP bloat slows down combat more than anything. Combat as it makes hitting easy, but enemies require multiple hits to kill. If a goblin requires two hits to kill at 90% odds, then that's 2 turns regardless. If a goblin requires 1 hit to kill but there is a 60% chance to hit, then that's, on average, less than one turn to kill. And advantage actually matters more when the hit chances are closer to 50-50 to start-meaning that this easy advantage with planned positioning and bloating HP favors enemies more than the players objectively.
(in addition to the uncommon dirth of actually worthwhile studded leather and chainmail, stupid half-plate favortism...)