How many mistakes is too many is kind of a loaded question but personally for me it's a matter of whether or not you learn from your mistakes in a time span of say 2 hours. I generally prefer not to kick people and rather just let them figure things out since advising others on how to do mechanics / play the game has always ended up going south because I know how to play my job/class which is fine and all but that doesn't mean you know how to do the mechanics on this fight in particular. After some passes I don't call people out, I simply say, "I'm gonna ask the person/deadweight who's causing wipes to leave. Not going to say names, but you know who you are." and leave it at that.

99% of the time to my experience that person knows who they are and they leave.

Aside from that matter I wish SE incentivized actual raid content for FC's . They're kind of pointless outside of buffs/crafting. I personally wouldn't mind raiding with my FC as opposed to leaving and joining new statics every tier.