Sadly I don't think you're far wrong. I was too young to appreciate Cooper, would have loved to have seen him. So I'd have to say Laudrup or Gazza. I think with McCoist his success was more down to the partnership he had with Hateley. Those other two could destroy entire teams themselves.
As was proven when his gardening leave was terminated - he walked into a pundit job literally the following day(s). His family weren't exactly going to be reduced to food banks and crisis loans.
No matter how you want to dress it up - it's abhorrent and inexcusable behaviour from someone who proclaimed a love for the club.
A decent man would have walked away.