We saw in Captain America: Civil War that Zemo used Bucky as a means to make the Avengers crumble from within.
When Tony saw the footage he was enraged and the Avengers literally broke up.
All I want to do is point to the fact that instead of using Bucky to make the Avengers fight among themselves, why didn't he use the other 5 winter soldiers,
Also, we know those 5 were stronger than Bucky and maybe equal to Cap if not more.