Its really hard to follow given how its narrated. So... lets try to sum it up?
MC is friends with a bunch of OP guys who run treasure hunts. MC himself has little to no skills compared to the rest, still, he's well liked and the party/guild decides he should be the leader regardless.
Party is so friggin' OP that everyone things MC is equally OP, not only because he _may_ be strong, but because they believe he's the scheming type, your regular Lelouch, even. In reality, MC is pretty smart but below average at best, and his common sense logic, while sound... is 99.9% of the times missundertood as genius.
As such, he leads the administrative work of the party/guild whatever its called. He has access to high class items and actually has a broad knowledge of the ins and outs of the job... which is why he knows exactly that he _shouldn't_ be there.