Considering there is plenty of discussion regarding balance, environment, etc, I think one point that gets lost is that BG3 and 5e are inherently different games.
5e is a collaborative game, where the DM and the party create a shared story and play together, whereas BG3 is a co-op game against an AI.
As a DM I would never make the game difficult for the players by focusing their Wizard constantly, even though arguably they are the largest target. Partially because I perceive the enemies might not do that, but also because that would make the game boring to my players.
Whereas the AI in BG3 has no problem throwing 3 flasks of alchemists fire at Gale putting him out of the fight before he acts. And I am fine with that, because the rest of the party will pick up the slack (particularly true in single player).
So I think since the encounters are different, so should some of the rules, and taking a completely copy of 5e rules would lead to a mediocre game.
Because 5e rules are (generally) simple and are just a tool for the DM to create engaging encounters tailored to the PC's. The DM has the flexibility to make the game engaging
Whereas in BG3 the encounters are tailored for an abstract party, so you need to tailor the PC abilities to fit these situations. The players need flexibility in this case, since the game itself is inflexible (albeit has a lot of choice). Therefore some changes to the game mechanics are needed to make it engaging.
Sure they can't run it like an in person DM could, but they could at least make the AI targeting less sadistically brutal. Currently they ignore everyone and everything just to focus on taking Gale out of the gam ASAP, including running through environmental hazards, triggering attacks of opportunity, and just straight up ignoring every single other threat that is in front of them to go straight for the back of the line and get at the wizard. This not only make the wizard impossible to protect, it makes tanks in general entirely useless. What's the point in buffing up my warrior's AC if the enemies will ignore them entirely to attack the wizard? Although considering they buffed a cantrip so much that it reduces AC by 2, I'm absolutely terrified of what acid spells will do at higher levels, so maybe having a tank is useless anyway because acid and AC ignoring surface effects will just nullify it entirely anyway, but I digress. Point is, plenty of other games out there have AI that actually targets the more reasonable threat or some kind of ability to let the tank actually draw aggro and do their job. If they need to make up a new ability to let the tank draw aggro, I'm all for it as long as it's well implemented, just something to make the tank actually useful and to save my poor squishy wizard.
