I hear what you're saying about greco takedowns (Randy's are beautiful, and highly technical), but thats not really what Brock does...he double legs guys but without changing levels, he just bends at the waist, wraps guys up and drives through them...like a football tackle almost. It definitely works...the man won a d1 championship doing what he does, and he's put all of his opponents on their backs. I just think it leaves him open to punches, and Carwin is tailor made to exploit that.
That's the image I always have when I think of Brock's takedowns.