I'll give you a c): a lot of their popularity came from Wolvie and Spidey being on the title.
And to all, I would say, so what? I never said it was a groundbreaking run like when Perez was on the title. In fact, I would be hard pressed to name one storyline that I would put ahead of any of his, or later, Busiek/Perez. But, using a sports metaphor, he put butts in the seats. And he kept them there for a looooooong time.
Look, I see the flaws in Bendy's run (and general writing skills) as much as the next guy (more, since I actually read them.) But, the fact that Avengers is so popular right now tells me that they were right to shake things up. And Bendis deserves a lions share of the credit.
Bottom line (for me): From a purely business aspect, Bendis gets an A+. From a creative side, maybe a C. Bendis had some good to great ideas on his run, which would have made for some truly memorable storylines if he had passed them off to someone with better writing/plotting skills.(Or someone not so in love with ninjas...)