Dude I think most of us forget that Tony had the reactor removed in im3. So when Bucky grabs it in the cap3 trailer the most it can do is shut down the suit.
oh no, I’m perfectly aware of that. that’s why it scared me so much. why Bucky wanted to shut Tony’s armor off? to stop Tony’s attack or to increase his own chances? maybe Bucky was being chased by Tony and wanted to shut him down to escape. maybe he realized he won’t win a fight when Tony is in the suit, and decided to cut the armor off, leaving Tony unprotected.