Not sure about that mate, he took his beatings like a man when he lost to Douglas & Holyfield. But yes when he wasn't as mentally strong as someone like Ali, Foreman, Holyfield.
Stylistically Foreman might have been all wrong for Tyson but the fact that Tyson carried knock out power in both hands, had a great chin and the fact that Foreman was in his late 30's, early 40's, makes the fight a fascinating prospect, it would have been a much tougher fight for Foreman than Frazier.