so with your logic, every time you meet a new companion if you have 4 already, one person must always just either leave/die/become an enemy? That's makes narrative sense to you?
No with my logic a companion's presence among recruited should be justified. And it can be justified for a while with the fact that we've just recruited him and didn't yet find what to do with him. But after some point it's option 1 or option 3, but please, not option 2.
Nope... Option 3 with them being dead is just cheap. Not effective narratively in my humble opinion.
I get very attached to my RPG companions and would rather they had something to do while not in my party, or if they die or leave, it should be because of the player's CHOICES having consequences. Not because of an arbitrary gate where the chosen party goes through and the rest just drop dead for no reason.
Sorry, but are you arguing that's not effective just with just your feelings? Implementation can be better, yes. But effectiveness lies in different part here - hoever you make them leave you can be sure no one will ask "why they are doing nothing?"