And I’d agree with you, of he didn’t come back at the Battle of Hogwarts to actively stop Harry. He chose to do that himself, proactively. He had to just go with the flow with the other people leaving and not sneak back.
There was a point after Half-Blood Prince where he could choose to change. There was a point where he had to see error of his ways between that and the Battle of Hogwards. It seems he took that step for a while, there was redemption arc brewing - but never happened.
He was indocrinated, yes. But he saw how terrible their side is and still chose to stick with it when he had a choice. He was 17 and adult in Wizarding World. Old enough to know right from wrong.
It is likely that some time after, he regretted it. Otherwise I don’t see Harry and him nodding at one anoyher in the epilogue. But at the time of the books, he was not a good guy at all.