IIRC Jen beat Champion because she worked out hard in her Jen persona so she was much, much stronger when she turned into She Hulk.
Right after she had to wear the Jupiter suit to regulate her strength, she was shown lifting Thing's weight machine on it's highest setting with one hand.
Well that and the fact that in the rematch Champion wasn't using the Gem... 😉
As has been said Drax even with the Power Gem got beaten by Thor.
It could be argued that Colossus with the gem would tap into it better than Drax with Drax being childlike and dumb at the time, although the counter argument to that is that Drax at that time had arguably a higher base level of strength than current Colossus.
Also Champion had beaten IIRC a number of high powered beings with the gem, including Drax, Gladiator, Surfer, and Beta Ray Bill (going off the guys I could see in the background being treated for their injuries in the issue)
But the counter argument to that is that Champion was already one of the strongest beings in the universe without the gem and an amazing hand to hand fighter.
And the fights were strictly hand to hand, no other powers allowed
That as has been said is the problem with gem arguments, no two users tap into them in the exact same way, so as we have never seen Colossus with the gem, we have no clue how well he would be able to tap it's power.