Not only does this sap the film of much force and lower its stakes, but it also reflects a pretty puny understanding of embodiment. Sure, the heroes of Soldier are fine physical specimens. They are muscle-bound and fit. The film's opening sequence highlights this by showing Captain America running at about 30 miles per hour along the Potomac, far outpacing his by-no-means-out-of-shape friend Sam (Mackie).
But the indestructibility of these bodies and their depiction as mostly machine-like instruments of war imbues them with a dehumanized abstract-ness. Aside from "human weapon" behavior, we never see these characters do bodily things: eating, drinking, sleeping. There's no charge of human-ness to these bodies; even the romantic chemistry that is occasionally hinted at feels forced, akin to the awkward human-to-human contact in Spike Jonze's Her. At one point Captain America jokes that he "had a big breakfast," but this is the only hint we get that he is in fact the type of being who needs to eat.
Part of what works so well about the action films of, say, Quentin Tarantino, is that they have a decidedly enfleshed aesthetic. Tarantino's characters eat and drink constantly. They are hungry and they seem to enjoy food (burgers, fries, sushi, strudel). They sweat, they fear, they are broken and can (and often do) die in all sorts of way that foreground the body's breakability. Not only do films like this pack more of a visceral punch, but they also support a more realistic view of embodiment and what I see as a more incarnational respect for physical reality.
To me, the pre-serum weakling Steve Rogers is more interesting that the fighting machine Captain America. The limitations of embodiment reflected in the former feel more real than the indestructibility of the latter. But maybe there could be a happy medium? Would it be too much to ask Marvel to make its god-like heroes a bit more fragile? And could we maybe have a few less fight sequences and more scenes where we observe the characters' humanity?
In Soldier, for example, a more developed romantic interest for "Cap" would go a long way. So would more humor. The whole "1940s good 'old boy transported to 21st century world" conceit could be mined for laughs much more than it is, making the character of Rogers far more relatable. The Iron Man films, it seems to me, do a pretty good job of making Tony Stark human precisely because they emphasize human sorts of things like laughter and (to a lesser extent) love.
Soldier is too concerned with setting up plot points and showy action sequences to go deep into any character's human-ness. Furthermore, there's simply too much at stake (future movies and billions of dollars for Marvel) to do something truly daring or unexpected.