I think that's a valid complaint--my own situation is a little different, I'm just annoyed that I can't better integrate my existing songs into Microsoft's own music library.
However, I suspect iTunes and Google Play would give me the exact same issue: for example, I have the soundtrack from Stand Alone Complex, which is organized as being composed by Yoko Kanno. I can play it on my phone just fine, because, well, it's on my phone (which is exactly what I want--I don't need music streaming sucking up all my data from my provider when I've got a 64 GB SD card).
However, I can't do anything about the missing album art (since MPATool only supports WP 8.0). Of course that's not really surprising, since Yoko Kano's not an American or English-speaking artist--it's not clear that iTunes or Google Play offer her music either. It's surprising when Danny Elfman, who is sold by Xbox Music, won't be linked to my own Danny Elfman music. There are lots of little gaps like that.
Then again, given the age and nature of my music library, I doubt iTunes would recognize many more of my songs (it might--or it might recognize even fewer of them). I would really like using OneDrive to sync music though.