Well, when you are outnumbered by monsters whom are born as trained melee fighters and they come at you in groups, it's hard to constantly win.
Also, did it mention how many orks and marines it was in that story?

Also, regular humans can do rather impressive things. You sort of contradict yourself when you say [i]"The only thing is training and conditioning, and that only gets you so far before you hit the physical limitations of relying on a biological sensory system, which humans are already pretty damn close to to begin with"[/i]
But then you say.
[i]"The problem is that humans suck to begin with, and being a better version of something that's not very good to begin with means you're probably not all that great."[/i]

Sooo, are humans good or not?

Also, the blood angels aren't notorious for their self preservation. Albeit not as bad as the crimson fists, but what can one expect when one's primary battlefield tactic is 'last stand!!!'.