Actually, funny you should mention it, because I read an interview (by Damon Hill!
) with Schumi and MS then said "The Benetton was so tricky on the limit, it had to be balanced very carefully. Alesi and Berger couldnt do that and that was why they crashed!" So yes, in one respect you have right, the Benetton was not t-h-a-t good. On the other hand, I read a book by Steve Matchett who used to be a Benetton Mechanic and his inside view from 94 gives the picture that the Benetton actually was equal to the Williams.
Lets put it this way: Schumi (and Senna -91, as you mentioned) were maybe not in THE best car in their respective years (91 and 94) but their cars were at least second best, and combined with the awsome talents of Senna and Schumi, I am not sure I would count that as "winning without being in the best car"...
Obviously it is really difficult to find such a situation, which probably means Damon, like the other F1 World Champions, was in the best car, like the other F1 World Champions. Proved my point yet?