I think people just have a hard time accepting Francis being good because he's a guy who is "just big and hits hard".
Like the whole PRIDE thing is just this romanticized - they're smaller and skilled/specialized so they must be better quality!
Francis beat a lot of good fighters. Even if some were old none of them were really "washed up" except Cain who was retired.
Most grapplers don't have the take down ability anymore to get Francis on the ground, and Francis has already proven that he can take out other big time strikers. His only real blemmish is a decision loss against Derrick Lewis, and he has improved since then (not to mention Lewis might be the only guy who can hit harder than Francis).