Bonac has beaten Dexter, Nathan, Roelly, Rhoden, Ramy ... sure, they weren't all in their prime on those occasions, but they weren't an absolute disaster either.
Bonac fought a tough battle 2 years ago against Brandon, and won last year against Ramy. Brandon and Ramy would win the Olympia a few months later.
That said, I don't like the flow/structure of either Bonac or Nick, I hope neither of them ever win the Olympia, it would be a disgrace.