He was. And I saw that in comics from the 1940s. Did he do the same when he was rediscovered in the FF comics in the 1960s?
Well, he rampaged quite a bit. Led his forces against the surface. Teamed up with Dr. Doom and the Hulk. No blatant loss of life in the Comics Code days, but he probably doled out a few black eyes at the very least. Many heroes have gone through a dark phase or two. But the context of domestic abuse seems far more horrible than all of the brutality other characters have had to redeem themselves for.
Given the culture of the 1940s as shown in pop culture from movies to the comics, is anybody really surprised that a version of Captain America separated from that time might be a bit of a bonebreaking, thinks-with-his-fists kind of guy as written in the Ultimates?
I wouldn't say the Millar version of Cap was simply an old-school John-Wayne man's-man type. I'd be fine with that. When I say "bone-breaking", we're not just talking knocking some teeth out. He went to a more extreme level of steel-toed-boot-through-the-face viciousness, as Millar characters are wont to do. Granted, he's no Midgnighter, but still....
Likewise, a Hulk that actually kills people when he goes on a rampage makes for an interesting modern take, but that's not quite shocking enough, so he eats people. I've enjoyed some of Millar's stuff (Authority, Wanted, Kick-Ass), but it seems safe to say that cynicism, cruelty, and anger are emotions that permeate everything he writes. I don't think I've ever seen a moment of pure, untainted compassion or kindness in any of his works. Admittedly, there's likely plenty I haven't read. Maybe when I get a chance to check out "Superman: Red Son" I'll see a change of tone.
To my way of thinking, a Cap that's just an inhumane thug that doesn't think twice about shattering and mangling his opponents like Jason Voorhees..well, which of Cap's qualities does that leave to admire? There's no shortage of vicious, take-no-crap tough guys in comics.