I don't think there will ever be IP sharing with creators. They're hired to do a job, and if they can't deliver their best in creating good characters and stories then they'll find someone else to do that job. I also don't think it's true that writers hold back from the Big Two - there's not really alot of indie books that feel like something that would have fit within Marvel. I think it might have been Ellis who mentioned something like this (or Millar) but when working with Marvel both created high quality original characters. Besides, the characters that become indie hits are usually something very different to Big Two material.
In theory that's right. Just like there's no bad bands, just bands with the wrong songs.
But I think there are bad characters. Characters with terrible designs, backgrounds, powers and stories. Properties that will never really work in a mainstream market. My favorite team books in all my comic reading are JLI, Guardians and Superior Foes. All populated with generic D list characters. And each of those books shined - even though they all existed somewhat as mocking the typical comic superteam, their appeal being the loveable loser angle. So lots of characters can be modernized and revamped. Reimagined in a fresh new way. And with that, there's some that will always just be terrible if put in a mainstream property.