It's all linked, right? That's the problem. At the highest level, we are talking about dpr (damage-per-round) which is affected by HP, AC, to-hit, weapon/spell damage, etc. Thus, an enemy AC reduction is basically the same thing as a PC martial/spell attack damage increase. Larian could have easily chosen to do the latter instead of the former for roughly the same effect.
The goal should be to affect the dpr of all classes/attack types equally. Which, for HP-affecting spells that don't allow saving throws, means buffing them to correspond to the to-hit bonus of martial attacks.
I think we're pretty much in full agreement. All the changes combine to make something exponentially worse.
Bards: yeahhhh they'll suffer a decent amount. The only redeeming factor is that, last I checked, advantage/disadvantage in BG3 partially stack. Like, if you get 2 sources of advantage and 1 source of disadvantage, you'll end up with a net "1 level of advantage." (This only allows a net 1 level of adv/disadv; 2 advantages are still only 1 level of advantage). I like this decision. I like this decision a lot.
This will allow for a bit more use of bard buffs/debuffs, e.g., high ground (adv) + enemy in darkness (disadv) + faerie fire (adv) will net give advantage.