Well by Tyson you could see the knee was really causing Spinks problems, he certainly wasnt at his best by that stage. That being said I dont think Roy ever beats Spinks @ heavy or 175. And Spinks was certainly the more accomplished heavy.
Spinks could have definitely hurt Roy aswell. I dont think this fight comes down to that anyway, Spinks just had the right mix of skill, awkwardness and size to negate what Roy brought to the table.