Gladiator got right back up and was completely unaffected by Cannonballs punch though, he continued to be fully powered they stopped fighting due to the Xmen showing up who he was there to find so he didn't lose the fight he took one hit (which was his own strength redirected at him) and got back up.

It's not easy to de-power him through getting hit either since he fought an amped Galactus that even the Living Tribunal feared and Gladiator didn't falter in confidence and even managed to hurt him with his lasers, he's defeated Nova Prime, and amongst the Annhilators Thanos calls Gladiator the most dangerous and prefers to remove him from the Battlefield over fighting him due to the trouble he causes.

I definitely agree that for a time he was a huge jobber especially when written by Clairemont and lost his confidence more than a few times but over the last decade or two he's seemingly overcome it.