Based on
A) being a much bigger guy (didn't start at super-feather, is obviously physically bigger than Khan)
&
B) not being chinny as all fuck. Khan got decked by Richel Hersisa, Michael Gomez & Willie Limond, all at super-feather. Limond near took his fucking head off. Prescott decapitated him.
At the very least, Brook is obviously bigger, & has suffered nowhere near the chin problems against tiny guys.
However much Canelo-manlove is spilled, no matter how much deliberately contrary "GGG ain't proved shit" fedora-wearing wannabe-boxing-hipster message-board shite is generated, Brook-GGG is still the better fight.
BTW: This is a side-issue, but I don't know if Brook beats Khan at welter. Khan might fight out of his skin & UD him.
But Brook is still a more viable, more credible fight for a middleweight. Not a viable, credible fight for a middleweight--the match-up still makes me laugh. But not as much as Khan at middleweight made me laugh.
Like life, boxing is complicated sometimes.