I don't think Motion went as far as he could in nailing his subject to the mast, but his friendship with Larkin might have held him back. In fact, he is rather defensive about the poet's racism and doesn't address the contradiction between his attitude towards non-white people and his taste in music. Having said that, Larkin was a poet who somehow managed to make poetry accessible for many people and in doing so produced some memorable and important work. Motion's exhaustive biography does great justice to the work and the context in which Larkin wrote. One of the best biographies I've ever read.
