Baldur's Gate 3

So the current stealth mechanics are definitely powerful, and if you wanted to you could solo the game with a Gloomstalker 5/Assassin 7 (though Thief 7 would still be better most of the time) extremely easily.

I never really bothered with it after Act 1 though. The game gives abilities, items, and consumables that break the action economy and increase damage beyond what could be considered reasonable for the levels at play. These items/abilities are also much less tedious to use than all of the setup work that goes into positioning the party for the type of ambush situations you describe.

That means it mostly comes down to how you want to play it. You want to be a sneaky boy, great you can and the game even rewards you for that type of playstyle. I don't really think it's broken though, unless you happen to be of the opinion that the whole combat system is broken, since it seems to follow the game's design philosophy of giving tools, a sandbox, and seeing what we make of it.

For a full stealth party I would run a Gloomstalker 5/Thief 7 Sharpshooter, Battlemaster 11/Rogue 1 TavernBrawler/Drunken Equipment, Draconic Sorcerer 11/Wizard or Cleric 1 Magic Missile caster, Tigerheart 8/Thief 4 DexGWM Cleave.

The game is as hard as you want to make it. If you think it's broken, don't use it. Simple as. There's enough food to long rest after every encounter. Do you do that?

It’s not really broken. Your party members are completely separate and distinct characters that can do whatever they want from a role playing perspective, including splitting up - arbitrarily adding everyone into initiative even if the enemies can’t see the other PC’s would feel less realistic and more videogamey. I’m saying this as someone who plays tabletop dnd and values the flexibility and near limitless options the game can accommodate. This is also a weird situation cuz many tabletop players have very different homebrew rules about how combat is initiated. Some DM’s allow people to opt into combat when someone else initiates, some DM’s decide who is in an encounter by distance, some force everyone into initiative when one party member initiates - there’s a lot of permutations and I think Larian did the right thing here cuz if you don’t like it and think it’s broken you can very easily not use stealth and line of sight to nuke your enemies. This isn’t a competitive game after all. I for one appreciate the tabletop spirit carrying over to BG3 instead of being unnecessarily restrictive.

What's broken for me after using Astarion for assasinations in the same place is the "enemy of justice" condition. They can smell him through every shapeshift, I changed the entire party to gnomes after the deed and still couldn't walk away from my crimes.

And here I always thought combat was proximity based, not just sight based. Is it really the case that party members remain out of combat until they are seen or choose to engage?

Setting the combat tracker to be based on proximity to engaged friends/foes seems like the simplest solution.

Yeah, I've always thought that mechanic was so broken. When one person initiates combat, the entire party really should just go into initiative. It's weird having certain party members be out of turn-based mode, like they were in a separate time stream or something.

Also I still don't understand the mechanics when you go into initiative from that state. Sometimes, you have an action, sometimes you don't and just have to pass your turn.