It's not that Brook is less loyal, but more that Zoro showed more loyalty moments (Thriller Bark, bowing to Mihawk for Luffy's sake).
Bowing to Mihawk in return for getting trained for 2 years and living in a cozy castle? OH NO, THE HORROR!
I don't doubt Brook or straw hats in general would do the same in similar situations, but Zoro being the most loyal SH isn't some scandalous take.
He's willing to overthrow his captain if the captain didn't have a genetic haki that is not in his control?
zoro never fought luffy either nor does he have a gag of hitting luffy what is this guy smoking?