An ambition of self-denial and competition is a somewhat positive description. Combining that with meagre makes it align with the general evaluation harmless little man, what Coombes was before his psychedelic experience with the magic mushrooms.

An ambition of self-denial and competition is a somewhat positive description. Combining that with meagre makes it align with the general evaluation harmless little man, what Coombes was before his psychedelic experience with the magic mushrooms.
Whether meagre is taken as insufficient or small and weak doesn't change the sense of the passage.