I think Best in Show was better than cute but no Princess Bride - true. But it's still a must see. Willard played the funniest character in the whole film. I crack up simply thinking of him doing his thing at that dog show. His delivery is flawless. When I first read your post I thought you meant he produced Best in Show but as I was writing how I thought he made the movie the light went off! Could not agree with you more. I do think Levy was quite special too - doing his thing, but nowhere near the lean genius of Willard's performance. Also think O'Hara is superb at what she does - such a natural.
We have to thank some of that crew for This is Spinal Tap too, though, which is also a masterpiece. Not as good as The Princess Bride, but before I knew of Princess Bride I thought it was a one of a kind gem - good old Reiner again.
Regarding the troupe, or overlapping performers: A Mighty Wind WAS the flattest of the bunch, imo, and none come close to Spinal Tap or Best in Show. Summary, Princess Bride beats all. True.