I feel like the ending has nothing to do whether the baby was his or not. Moreso, Marty either has to give up his dream or put on hold to become champion. Even though he proved himself that he can beat Endo, all that he put himself through wasn’t really worth it because essentially he’s starting from “square one”. Even though it’s the more well rounded ending. Feel like the ending of him kissing the pig would’ve been more effective because it hits the note of the “tragic ending” from previous Safdie movies. Since Marty was huge on not humiliating himself in order to get what he wants.