>>115623236He really was in a shit spot. Going back to the past means erasing every character the fans love, but staying would mean inflicting suffering upon billions of people, including his own parents.
It would have been a nice arc if he reconciled with his failure and stayed in the future, but you can't justify it in terms of human lives. What really shits me up the wall is that he went for the "bittersweet" ending, while I think the majority of fans just want Jack to be happy. He's suffered SO much, and then Genndy really fucking twists the knife in.
Frankly, I think S5 should have focused more on the Aku/Jack relationship. They hate eachother, but they're also the one constant in each others life. In the end they never really interacted.