Hmm...that said, Roy leads our team, and the arguing and criticism there is pretty serious.
I have never thought that Tarquin didn't lead the team in the sense that he was subordinate to anyone else - it seems to me that he probably IS the planner in the outfit, it's just that he can't give orders without a rationale. Maybe that make him not a leader. Hmm. I suppose that Roy can give orders without explaining (can't think of instances, but there you go), but there is a reason for that: half the party is definitely NOT any good at leading by virtue of Durkon being, well, congenitally unable to lead, and Elan and Belkar being Chaotic+daft/psychotic. Haley can plan, and V is intelligent, but we know in what ways they aren't cut out to lead.
My (rambling) point is that just because Tarquin's gang of friends are sarcastic and critical doesn't necessarily mean that they are cut out to lead, so he may plan, organise and run the group, but as more of an administrator than the traditional gung-ho, follow-me type of leader.
I feel that his delusional nature about his own importance doesn't have to require that he's wrong/lying about his position in the party - just that 'leading' that party means something other than dictating to its members what is to be done. (Blah blah blah - sorry, thinking aloud here...)