Every time I've participated in a randori, the attacks were graded to the capabilities of the nage. I've never seen any dojo where a low ranking aikidoka was expected to go through a randori, as Daniel says, "full contact, full speed, full power."
We do Randori quite a bit in my dojo, and usually the randori in the shodan tests are impressive by my standards. Nevertheless, I think that we still stick by the idea that if you are attacking in a way that nage can't handle, then your uke needs work.
This, of course, is completely separate from the question of whether stress is a productive learning tool, how much of it is appropriate, whether that applies to randori in different ways than other aspects of Aikido training, and whether getting bloody is the most effective way of engendering stress. I'm afraid I have no opinion on any of those questions except that they are sort of interesting.