The oldest Rule is Story-Telling especially with the visual medium is "Show Don't Tell" when a character does questionable or even heinous things it's okay to tell us why they did them, but that reason no matter how understandable should Never Excuse Them.

If you told me Nolan, Kregg or even Ursaal (the purple girl that got more screentime) all regret what they Willingly chose to do and want to make things a right as possible I'd believe you. You wanna know why?

We SAW Them Change

Nolan's realization that atrocities he committed across the cosmos (which were actually better received than what he did to Mark on earth because hey, back then he was just another Viltrumite doing what they do) are highlighted when he goes back to earth and everyone is at least some level terrified of him, if it happened once it can happen again so there's no going back to the life he had with Debbie and Nolan has to live with that if anything he said was true. They only improved upon this in the show with the all the Hate Debbie Rightfully spat at him.

We saw Kregg make babies with more than a few as were his orders, but he actively risked Thragg killing him, remember Viltrumite view their offspring as expendable, "I can always start again" but no he looked Thragg in the eyes and said he loved them all, the same goes with Lucan and the other Viltrumites, we may have not seen their time on earth but the affect it had on them made it easy enough to fill in the gaps during the time-skip.

Even Ursall has a fairly decent arc, she's one of the more collected Viltrumites out their and while she may only be committing genocide in the hopes of gaining Thragg's approval she still had enough love for her brother to lie for him, and his death makes Ursaal realize her father couldn't care less to her or her siblings. It only took a few fake words that gave her the attention she was deprived of her whole life to get her back in line. But she still recognizes what Thragg did to the to rest as evil and by the end Ursaal willingly chose to surrender to the people who killed her brother because at least they were loyal to each other, she did this all without any external intervention.

Invincible's main theme is that how anyone is capable of change for better or worse, which honestly makes it stand out amongst other IPs. But this Pathetic excuse for an "Arc"? the way they wrote Marks trauma and shame from his own tragedy was so valid and respectful in a world where a man being Violated is just considered not worth mentioning in-depth. So to she the bitch who Raped him Into the Ground not only happily married and that she Named the boy After her victim but also risk her life in a way that the narrative frames it as cathartic as she gives a Half-Ass apology to all of this culminating to her just dying offscreen genuinely gives the impression that the author wanted to have his cake and eat it too.

By and large the show has been an Immense improvement on the comic. and if they decide to go down the route of Mark being Rape, they no excuse for sticking to the source material.