Totally agree with all of your points. I want to address few things in this thread. Some major spoilers for Divinity: Original Sin 2 and surprisingly for Mass Effect 2:
Arbitrarily locking your party Vs party members leaving because of your choices - the later is more than ok, it makes sense. If you did something that a certain party member was against so much he doesn't want to keep traveling with you, it's fine. It makes the party members more believable as characters and emphasize their personalities. And it is a real consequence, it is a direct result of your choices. But when you arbitrarily remove all but three of your companions there is no real choice or way to remedy it. You strip choice from the player, make the companions a stupid NPC's that has no control over their fate and break immersion.
Someone mentioned me2 and I think me2 is a GOOD example of how to do companions deaths. First of all it happens in the end of the game, and secondly it is based on your choices during the game and in the final mission.
Divinity Original Sin 2 and why I really don't trust Larian in this aspect of game design. I wrote about it briefly here on the forum but it deserves a more organized summary: divinity Original Sin 2 handling of companions was the worst I ever seen in an RPG video game, and it looks like the companions design actively sabotaged the narrative.
At the end of act 2, right before you enter the temple to fight over who ascend to divinity, you have to talk with all of your companions since all of them are potential rivals in this fight. If you treated them well throughout the game, they will side with you, but if you ignored them and didn't do their quests they will fight you for Divinity. Sounds awesome right? It is, except 3 of your potential companions died much earlier in the game in a very silly and senseless way. But Larian wanted to eat the cake and leave it whole, so they made the three dead companions into zombies and made them fight you anyway. This decision is one of the most stupid decisions I have ever seen in a narrative driven video game. I can't think of any explanation for aside from "Larian wanted you to commit" and I'm pretty sure this decision was done without involving the writing stuff until later into development. The only other possible explanation is that initially the companions were supposed to continue with until the end of act 2 but they changed it at the last moment. Otherwise I can't explain this terrible writing.
This is my problem with their insistence on "committing" to a party. They did it so poorly in dos2 that I have no reason to believe they will do it right this time. Just stupid
