The Redskins had a guy who went from (at times) looking like a franchise guy to being a pretty average to bad QB. That franchise is horrid, and the ownership is bad, but if Cousins gets paid it's not because the 'Skins let a top ten QB walk.
We can make a really long list of guys who had some impressive seasons and even impressive runs who, at the end of the day, aren't legitimately top ten type of guys.