[Zenbit_UX]

Yes, you're right, there's a possible third category of leader by necessity but it could be argued that this is a subtype of leader by title which is why I didn't understand your comment on first read.

Maybe leader by "position" or "circumstance" is a better term as it covers the situations like "most experienced in a team" even if that experience is only a few months more than the person they're helping and even if they don't have the title to match.

I still agree with the parent commenter that distinguished between _true_ leaders and those who've been placed or defaulted into the role.