I don't disagree. I just haven't seen any evidence from Nokia, based on their own UIs, that they can make the WP7 UI more desirable, rather than less or the same.
I think this argument could go either way. As a "commodity" WP7 phone maker, Nokia might be able to get 20% of the WP7 market on brand recognition alone. But a crappified version of WP7 might earn them 0% of the market instead.
As someone who values a fairly broad oligarchy of phone ecosystems, I'm frightened that Nokia will have 20% of a WP7 market that is perhaps a little more than one or two million devices per year, and stagnant.
WP7 (or 8 for that matter) isn't going to be helped in this kind of scenario by a bleeding vendor that can't sell more than a few hundred thousand devices. As consumers, we're not going to be helped by the death-by-a-thousand-downsizings of Nokia (a business that has a good record otherwise of innovation in technology and market development, at least until the last few years) and a side show of a user community that can't support development of innovative software and business models.
Actually, they could line up a couple dozen WP7 phone manufacturers and still fail. What they need is not manufacturers, but people buying and using the phones. This is not happening.
If they do it, they'll be a commodity phone maker and will have to compete in price with other WP7 phone makers. All three of them.