Given that you can get cw behavior with ce, I don't really think the original breaking of cw was reasonable (though I expect it went the other way and cw existed before vi settled into its current verb-noun philosophy).
I agree with you on the doublings - probably makes most sense to preserve them.
That is a reasonable argument against the existing cw behaviour. I consider this to be a reasonable argument in favour: when you delete a word, you probably also want to delete the space after it; when you change a word, you probably don't.
There are reasonable arguments on both sides, and I don't think that the balance is overwhelmingly on either side, so I consider either choice to be reasonable.
(In general, to show that something is unreasonable, you can't simply present arguments against it. You need to show that the arguments supporting it are weak.)
I think that argument would be much stronger if forgoing deletion of the space was hard to do - but it's literally one key over. Further, it mucks with peoples' intuitions about what range w actually covers - something I'm only recently overcoming after 20+ years with vi and vim.
Meanwhile, I have found myself in the position of wanting to delete the space and had no way to express it (as a single action that I can redo with .).
I agree that cw violates a pattern, but I think it's a reasonable violation. (Not necessarily good, but reasonable.