this but rossiu was a traitorous little bitch who deserved to be executed
How so? From the beginning he acknowledges that he's not Kamina, not Simon; and has been trusted to do things by those same people because he doesn't think like them. When push came to shove and he was given the impossible task of saving humanity, a guy without a ton of spiral energy, he tried saving as many people as he could in his own way. He knew that his friends wouldn't like him for it, but he also knew Simon would, and he did, understand why he went that way.
He's not the main character of Gurren Lagann, he's a someone who belongs in Gundam or LOGH. And so he tried to go the most reasonable route in a world where the more unreasonable you are, the more powerful you are. He never once betrayed Simon. Do remember he was appointed that position by Simon to do exactly what he did.
At the end Simon wins out simply because... It's that kind of world. The best he could do is not the same as the best Simon could.
I understand you're likely just being exaggeratory/trolling because lolrossiubad, but I think that whole arc was incredibly well written, honestly a standout piece of super robot directly criticizing real robot.