I think the idea with Thanos vs Hulk is that their strength gap wasn't as far apart (presumably Hulk is stronger) but Thanos was using actual fighting and boxing techniques, whereas hulk usually just smashes. Like how a skinny martial artist can take on someone much stronger than them, technique makes a huge difference.

That said I felt really robbed we never got a BannerHulk rematch with Thanos. Him being intelligent would've let him actually train his technique over the timeskip and complete the character arc.