Gladiator Outedges against all not in strength & durability...all of them by far are on par with Kallark physically, but are superior in durability due to a better healing factor.
Gladiator edges in:
-Skill (Not against Skaar though)
-Versatility (far more powers)
-Range (far more range abilities).
I say Kallark can beat Hulk and maybe Ross Red Hulk, but perhaps not Skaar due to Skaar's boost with the Oldstrong power.
They just wanted less competition for Cho, that's why they (momentarily) killed Banner too. Now we have 4 "Hulk" around in the main Marvel universe: Immortal Hulk, (She)Hulk, Brawn (Cho) and the second Red Hulk