I don't know if it is fair or not but I kind of just lean on mystique for this. I'm just not well enough informed to make my own case. Marciano's a good example of a man the men he faced probably should have been scared of him but simply were not. Dempsey's an example of a smaller man sending fear through the division Sullivan, Liston, Tyson, dudes were scared of. Ali and Butterbean, dudes were not scared of but probably should have been. I can't hardly remember. It's funny, what happens when you are young you never look up because you feel like you know it, but really, I should look up Valuev's career. I can't remember folks being scared of him either but maybe they were. I don't remember. Wilder if you believe him, everyone was scared of Deontay including the men who beat him. If they have that fear mystique to their story, i'll treat them like a scary dude. But really, it's kind of hard to believe pro fighters are scared of an ass whooping. So, i'm just giving it to them based on like consensus merit. I don't know who, like behind the scenes, was scary and who was show or promoters' stories.
Reminds me of a story I’ve related here a few times, told by Randy Shields. He went out to ring center for referees instructions when he fought Thomas Hearns. The Hit Man met him with the death stare. Shields said it was all he could do to keep from laughing. “What was he going to do? Hit me? He’s going to do that anyway.” Shields was a genuine tough guy who didn’t look so tough. Went 15 with Pipino Cuevas, beat Ray Leonard and other top guys in the amateurs. Took on all comers. Hearns stopped him on cuts and never iirc really had him in trouble.
I remember watching an Iran Barkley fight on TV, and somebody in the room said of him, "I came, I saw, I Ran", obviously in reference to his appearance. Scariest in terms of having to deal with them in the ring would be Roy Jones. Tremendous speed, very good power at 160 & 168, elite reflexes, and extremely unorthodox. Seems it would be difficult to find sparring that would prepare you for that. Dude seemed almost untouchable and went long stretches without losing a round.