TheVaultDweller
Front line cannon fodder
Well, he did shoot Angel out of the air during First Class, and she was fairly nimble. Plus, he can just spam beams and move them in wide arcs.
As for blocking the shield with his beams, Cap isn't stupid. The moment that shield leaves his grip, he is likely going to charge Alex and try to close the distance while the latter is focused on the shield. So, there is a good chance that by the time he has avoided/blocked the shield (if he can), Cap will be right on him. And in a close up confrontation, I would give Steve a decisive edge.
I know Cap is normally a more defensive fighter, but this is a scenario where I think taking a page from Winter Soldier, and going with overwhelming offense, gives him a much better shot at a win.