I disagree, in my experience players who consistently get 5-6's won't magically turn into a 8-ish rated player. They will get 7's now and then, but the bad ratings will return.
Agreed. There are some who promote the 'stick by your player' doctrine, but I am a 'dump them if they don't give me what they need' sort of guy.
Love the one you're with, if they play well.
If not, get someone else and love them instead.