go back and re-read what I said. I didn't say 'what's the big deal with if you've taken ukemi with the masters of this art or not' I said 'what's the big deal with how high a rank you've been tossed by.' High rank doesn't necessarily mean skilled. Just means you managed to pass a test.
Example from my own dojo, there are several brown belts. 2 of them are very skilled, very good at this art and 2 of them are about as clumsy as the beginners. However they're all the same rank so based on the logic that the higher the rank the bigger the deal to have been thrown by them, they ALL should do about the same job of tossing Uke.
I don't know your experience with higher ranked aikido practitioners, and I'm not questioning that, but I sincerely believe you would be hard pressed to not see and feel a difference between the way a very experienced aikido practitioner (such as a shihan) throws someone and one of their students (however experienced) does. All I can say is that I have felt and seen a difference between them. You are right that in most cases rank isn't as meaningful between kyu and lower dan ranks amongst various schools, but the difference between those ranks and , say, shihan can be remarkable.