It's hard to compare boxers and UFC fighters because UFC fighters don't have the luxury of picking and choosing their fights. A boxer's management can pick and choose and turn down any fight they think is disadventageous to their client.

In the UFC, there's one matchmaker, who's only objective is to make great fights that the fans want to see. He could give a fuck less if a fight is disadventageous to you.

To put it into context, Weidman is a beast who - if MMA was like boxing - would have been the guy that none of the top guys would have touched with a ten foot pole. The lesser known guy who is a huge risk with little reward (think: Golovkin until recently, Paul Williams, ect). Unlike Floyd Mayweather, Anderson doesn't get to say "no I don't want that guy, give me the easier guy who will make me more money." He had to fight every killer they put in front of him. So for him to go undefeated over a 7 year period is nothing short of legendary.