I think a 10 point system is fine, but I think getting actual feedback is useful for most people. And you're free to disagree (both on the usefulness of feedback and on the actual feedback.)
There are a few places that do mixoff type competitions that use a voting system to determine winners, which is cool. But this forum was built around the idea of sharing ideas and knowledge, along with providing access to a lot of multitracks for practice.
I don't think criticism is something we should fear or avoid. If you're going to mix, you're going to hear criticism from clients, other mixers, etc. Learning to hear that criticism, decode it, and make adjustments is a key part of the gig, I think.