I do agree with the person you're replying to, in that I'm not a huge fan of DnD mechanics - "works ok-ish" is what I would also say about them. It does do its job just fine, so this isn't a big issue by any means.
Related to game mechanics in BG3, my personal issues are as follows:
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Heavy reliance on RNG in combat. In turn-based games, I always prefer game mechanics which work as I planned, maybe with small variance (i.e. look at Advance Wars). Basically I prefer when my planning is the part determining how the combat flows (damage or cc? Which target? Where do I move to?) - there'll always be some "I'm not sure what happens on next round" due to just not being able to know what the enemies will do on their turn, so I don't really need even more RNG in the form of hit/miss (& save) rolls. Basically: chess is a good game as it is, I wouldn't want to have a 50-50 coin toss determining if I can kill a unit or not.
- I do think that some form of randomness is fine, but I don't like that there's just so many layers of RNG in all things. Damage abilities: first roll if you hit or miss, and if you hit, then the damage variance is often like 5d6 (5 to 30) - it's almost like doing two rolls to figure out if you actually deal any notable amount of damage or not.
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Practically everything related to the resting mechanic. I really feel like I would enjoy the game more if I just had fully recharged spells (and other stuff) in the beginning of any fight - and obviously then balance the game with that in mind. Where needed, devs could tag a certain area as "no resets here" so you know you'll be forced to do a couple of fights in a row without resets.
- One reason making me think this way is just the amount of available food, since you get more than enough resources to do a full rest after practically any fight anyway - so now it just becomes a QoL issue. It's not "do I want to use my resources to reset here?", in practice the choice is just "do I want to spend a couple of minutes going through loading screens?".
- If there was less food available so that you'd need to be careful about when/where you do a full rest, progress through the game would be: go forward until you fail a fight, load the game, do a full rest, fight with full resources - this really doesn't sound fun in practice. I don't think there's a way to implement this style of a resting mechanic in such a way that I'd personally like it (at least without changing a lot more about the game).
I do want to finish this with another disclaimer that I do think BG3 is a great game, and these are really just minor issues - I completed it yesterday and enjoyed my time for the whole ~120 hours. But my two biggest issues that I can point out about the game's mechanics are both just base mechanics of DnD.
Yup, I have to say that I completely understand why some people like it - it adds to the chaos, and your job is to mitigate/control the chaos (by eg. choosing to use Magic Missile like you mentioned). It's just not something I personally enjoy. :D