Why is Captain America so weak in Civil War?
I solemnly swear I will not make this answer sound like it has been written by some who is on Team Iron Man
First Captian America wasn't weak in Civil War he was just surrounded by too many super heroes who had power super human powers than him or a IQ infinite times higher (Tony) or training much more intense (Barton and Natasha). Amongts all this he was visibly weak.
The true super power Captian America has is that he is a great leader. ( Captian..Duh) So in the avengers movies he is the one commanding the super hero batalion and leading them to victory.
The case was opposite in Civil War he had left his leadership position for his friend and that disassembled the Avengers.
With so many super heroes against him, his powers were seen considerably weak.
Nevertheless, he is The Captian America and to be frank it was his movie .. and it did not disappoint the TeamCap fans. The witnessed the jaw dropping display of strength when Captian single handedly stopped a chopper from taking of, Plus he did manage to pull down Spiderman (who was equiped with Stark tech)
If there was a hero displayed weak in Civil War, then it was clearly, undoubtedly be VISON. With reference to the Air Strip sequence he was shown too naive and too afraid to fight.