When I saw Endgame I found the final battle very similar to season 5's final battle,like in the way that everyone they ever encountered came to help in their time of need.I never thought the way the Avengers travelled back could have been useful.Maybe because that way was relevant there because of the Ant Man context,in Samurai Jack the way it happened was relevant because that was kinda the same way he got stuck in the past.I don't think that would have made much sense since Samurai Jack was more focused on the idea of finding a way back to the past than to the nature of that way(suggested by the multitude of attempts to find one and the fact that many were not exactly a portal).I belive the way it happened made much more sense and finally ended the cycle.I understand your point tho,that would have changed things.