Captain America Is Miserable In Season 9
Captain America had a best in slot agenda pushed for half a season, and because of that, received a survivability nerf when everyone else got buffed in season 9. The damage output is so high that Cap is borderline unplayable, and other dive tanks just do his job better.
I think some buffs that could aid Cap in the current meta to make him a more viable and fun character again would be to:
Revert his shield nerfs, giving back his shield from season 0. It's a paper plate right now, but giving it more health and faster regeneration could be a very useful buff for him.
His team-ups need some work, they're some of the weakest in the game. I think having Voltaic Union from season 0 would also be great, better than this piercing one by bringing back the ricochet (but keeping the enhanced explosions). Stars Aligned has a few problems which could be fixed, such as failing to apply bonus health to the targeted ally, being easily interrupted by terrain as minimal as a small staircase or slanted ground, and being significantly slower when used in the air.
Alternatively, the dev team could nerf damage output, but I think this is unlikely.