The Boys has many flaws but A-Train's arc was incredible
Pretty much every character in the series is improved from the comics. But the two biggest examples IMO are A-Train and Soldier Boy. A-Train starts the series running through Hughie's girlfriend Robin Ward. While it was an accident done when he was high on Compound V, we're later shown him laughing it off with a friend. Throughout the rest of the season, we learn other horrible things about him like how he gave Compound V to terrorists and even see him kill his girlfriend Popclaw, even if both of these were done under Homelander's orders and due to pressure than real malice.
But when Hughie and Starlight save his life, and he eventually gives them the files on Stormfront at the end of season 2, we start to believe he's coming around. In season 3, he's shown trying to help black people in the community after his brother Nathan tells him about Blue Hawk. Combined with Homelander constantly abusing him, you'd think he's going to redeem himself by helping Starlight and Supersonic, only for him rat the latter out to Homelander.
But this isn't a moral event horizon but a moment of regression, just like we see in other good redemption arc's (Zuko, Vegeta). Because when Blue Hawk instead cripples his brother Nathan, and A-Train demands justice, Ashley reminds him of how he had no problem when he got away with HIS crimes. A-Train is able to self-reflect because of this and genuinely apologizes to Hughie. He knows what it feels like now. He kills Blue Hawk, fully expecting it to be the end of him. But then he's brought back, know having the latter's heart. Nathan is disgusted with his actions and kicks him out. And he truly sees how much Homelander doesn't care for him when the latter kills Black Noir only to remind the rest he was worth more than ALL of them put together and he doesn't need them.
In season 4, we can see A-Train is changing. He refuses to kill Todd and the other Homelander fans, a far cry from the season 1 A-Train who killed his girlfriend. He helps free the innocent Starlighters with nothing to gain from it. He saves Hughie from Homelander and even gets Compound V so he can save his father despite fully expecting Hughie to never forgive him. And when he saves MM and sees a kid smiling in joy, that's when he realizes how much he likes being a hero. Him exposing himself to save Annie and Butcher and going back for Ashley is a tremendous way of showing his growth.
And then we see in Gen V season 2 and season 5 how he's helping Annie in the resistance. Keeping his family safe too. He's finally made amends with his brother. So its >!tragically fitting to see him return to save Hughie and MM, knowing Homelander will target him. When he sees an innocent woman walking across the street, one who looks like Robin, this time A-Train IS running for his life and the woman IS in the middle of the street. But he dodges her, refusing to take another life. Having him stand up to Homelander at the end and laugh in his face was the most badass way he could have gone out.!<