I think pretty much any game can be min/maxed. I mean, even noughts and crosses has an optimal move in any given stage of the game. And if you want to do that, if making the numbers get bigger most quickly is your thing, fine, knock yourself out.
Where it crosses the line, IMO, is when it goes from ‘I want to play the game this way’ to ’I want YOU to play the game this way, or I’m going to be a dick to you if you don’t’.
Obviously, the game can encourage or discourage this behaviour in a variety of ways. As Gordon suggests, it can make the ‘cosmetic meta’ different from the ‘performance meta’. Or it can tune what loot people get from end game activities to specifically their contribution, not the entire party performance.
If someone is just literally tagging along without doing anything, freeloading to get the reward at the end, fair enough, boot them - that’s not on either. But ’I want to get this thing from this activity, and if you aren’t going to make as big a contribution to me getting this thing as I like, I’m not going to let you play’ is just, IMO, rank selfishness.
I mean, fundamentally it comes down to the same issue as a lot of other stuff - some people on the internet are just dicks. But you should try not to be if possible.