Hard to tell where to draw the line.
Margarito ripped off Lujan's ear, how often does that happen? And many a fighter have had their retina detached. But the injuries that ensure me sometimes it is the fighter's power would be the thrashing Briggs took against Klitschko: a broken left orbital bone in Briggs’ face, a broken nose and torn left biceps.

A Fighter's trainer signs off on gloves.

And most important to me is that some fighters break down easier than others.

Maybe Saunders got a broke face because he finally faced a menacing puncher. Defeating Martin Murray before this title shot didn't mean he was deserving IMO over a Charlo or an Andrade. But it is what it is, Billie got to the big dance and learned the hard way.

If you can't roll with the punch, you're probably gonna bare the brunt of the punch. Perfect punch to do it- as he was in the perfect position for maximum impact now that I've seen it.

Side note- I felt that James Kirkland was a pretty decent puncher, not menacing, but he could bang- But in the ring with Canelo one could see a difference in punching power.
A big difference, not sure why it was so apparent against Kirkland, but not Mayweather other than how Floyd positioned himself when he did get hit.