I mean, Thanos isn't even that tough. Most of the people fighting him were just human+ power level (notice how they specifically de-powered the Hulk for that fight?). A lot of characters could take him relatively easily.
Somebody mentioned Kerrigan. Yup. Zeratul would 'Nothing Personnel, Kid' the purple guy. Talandar (formerly Fenix) could fuck him up in a straight fight - the dude has died twice, he ain’t afraid of shit. All of the Zerg charcters, probably.
The Doomslayer, obv.
An entire collection of characters from Diablo. Good old Tyrael would bust him open, but any of the angel or demon characters could do that.
Kinda want to put him in a room with Jack of Blades. Nothing kills a supervillan like another supervillan.
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.
Asura. Asura's Wrath wasn't the greatest game, but it was memorable, and I'm pretty sure this scene makes Asura a contender for pretty much any match up.
Havent seen him yet, but doomguy would absolutely fuck thanos up. Mans killed one of the strongest beings in hell barehanded and stopped the demonic invasion of earth in a matter of weeks.