It makes no sense for him to be fighting red hulk with no green hulk.Why couldn't we just get a new red skull and Hydra instead? He can't block with no powers he would get crushed and his arms would break.

The plot hole is the show runners forgot what they did. Season 4 is filled with plot holes and random facts/things no one question when mentioned such as "Hey Luther thanks for watching me in the moon" no one asking anything about it or the fact their father and his wife are aliens. This season felt super rushed and it sucks it was only six episodes. The ending sucked they could of existed as long as they had no Powers and could figured out a way to extract it to save all their lives then toss the container into the monster at the end. Another plot hole you can't save your family if the parents never existed the children were never born. They said it would effect all timelines so no one not even their kids loved and loved ones lived. What a disaster of a season and ending for these characters they deserved better.