I don’t know anything about Charlie Brown, but I’m not sure constant bad luck and disappointment capture the spirit of the British humour being discussed, as that can just as easily be used to describe slapstick humour. Perhaps it’s the existential futility/resignation that’s missing? Charlie Brown is a child, so they perhaps have optimistic naïveté instead (such that their failure be viewed with pity instead of kinship, which is really the distinction here).