One of the few failings of Captain America: The Winter Soldier was the lack of real beef given to Brock Rumlow, the SHIELD/HYDRA operative who acts as Alexander Pierce's muscle and will, at some point, turn into the Cap's enemy Crossbones. Frank Grillo described the role as that of someone who "pretty much beats the s*** out of everyone in the movie and that's really it". It's not exactly Othello, is it? His character arc is just a perfectly straight line, at various points along which he kicks someone else's head in. He's the Captain America equivalent of that really beefy blond dude who keeps trying to see off John McClane in Die Hard - all he is is really, really good at punching people in the face with next to no explanation as to why or how he came to be so incredibly fascinated by Pierce's idea of providing freedom through control. As it is, it just looks like he's a complete thug, a proxy villain for the Cap to fight while Pierce is otherwise occupied. Yes, he did have to be in it so that Crossbones can become a future villain, but it would've made a great deal more sense to just slip in a couple of lines here and there to let us know that he does actually think and feel anything at all.
