A driver doesn't have to win or even finish a race to show he's better than his car suggests. Besides, engine failures were a fact of life back then, everyone had to deal with them (possibly except for anyone driving a Ferrari). At any rate, when he did finish the results weren't great and he hardly outdid his teammates.
I guess I sound like I'm being too hard on the guy, maybe I am. But tbh I'll never rate him as any better than any other midfield trundler that won a race occasionally, and to be fair there's been plenty of those over the years.