"With Fedor, you have over 30 fights against top-flight competition"
He never fought in the UFC. He has never, ever, fought top-fllight competition in their prime. I don't care how many of his fights people list. If you don't fight in the UFC, you're not fighting top-flight competition.
Cain will not "run through" the competition in that division as the Heavyweight champion. It's the nature of that particular weight class. Championship runs are short-lived.