But he still did nothing though. He accepted the lead atmosphere plan and then left earth. That's it, that's what he did. He didn't come up with it, he didn't press the button... he just stood there and nodded. How is that a sacrifice? And going along with the plan... did he even have a choice? "Wait you mean I'm gonna die if we do this?? I mean I know my mom and her friends will probably murder most humans and then enslave the survivors and you could stop it all right now with the lead but I'd have to die??? How dare you. No, terrible plan. Figure something else out" See, it's ridiculous. Anyone would go along with the plan. It's not a sacrifice, it's just doing what's right, it's being a decent person. What Kara did was a sacrifice, choosing to press the button and murder/banish hundreds of people including a man she loves to save her city, wrecking her identity and humanity in the process. Lol even Lillian sacrificed, actively having to put aside all that she stands for and her views to have an ally in an alien for the greater good. Mon-El did nothing. Please, tell me what he did that makes his leaving a sacrifice and not just him running for his life.
You're right, Rhea is guilty of the invasion, can't blame Mon-El for that. But it's true that he knew what his mother was capable of and he let her do it all even though he could've stopped her several times. He could've done some real self sacrifice and gone to Daxam to become the king to his people instead of hiding behind Kara and the DEO while his mother's ship floated above earth. He was scared and selfish which is understandable I don't blame him for that but still his behavior made his crazy mom snap and do all the stuff she did and he could've stopped it since the very beginning.
Honestly the only thing that bothers me is how the producers and actor treat what Mon-El like it's something so noble and heroic when it's just literally the only thing he could do.
I don't think he's a bad person. I think he has good intentions. But he doesn't deserve to be called a hero or treated like one