Paul - I'm not trying to put too many handcuffs on this question. We each have an opinion on what we have seen, heard, and experienced. Based on that - what are your thoughts? I have taken ukemi from Yamada Shihan and Kashiwaya Shihan.
Taking ukemi from someone isn't a worthwhile gauge of ability, in my opinion. There's still an amount of cooperation in some form or another. I'd only comment on someone's ability if there was a dynamic situation that involved no cooperation --- and I haven't had that with O Sensei, or anyone who trained directly with O Sensei. So I cannot say how "good" they are, and I've no desire to engage in speculation based on what someone may have said.