Baldur's Gate 3

That is correct. Although many, many tables have that as a homebrew rule too.

That's correct that it's considered an action in 5e. The idea is that your turn represents about 6 seconds. Bonus actions tend to be quick nearly instant actions or things that can be done while taking your action at the same time. And downing 8 ounces of liquid typically takes some time and can be distracting. But in a lot of games (The ones I run included) house rule potions as bonus actions because it's just more fun to keep the game moving. BG3 does a lot of things that are more house-rule type things meant to do this exact thing. It keeps the game moving giving you more time for the fun parts of DnD. They give you access to a lot of spells earlier and make them easier to use to get rid of that early-level slog that's common in most games. I personally love those early levels as it gives you a chance to develop your character before making them a straight-up killing machine. But that's not really how video games are built, so I'm really happy with the streamlining they've done in the game. There's even some stuff I'm going to bring into my own future games.