Couture can submit Machida because Tito almost got a super lucky triangle on him? Couture has only ever submitted two guys in MMA and one of those subs was the first fight in his career. I don't think he has the tools to submit Machida, a BJJ blackbelt and a seemingly decent one.
Tito Ortiz has really good BJJ skills people dont know that because he would rather smash you with elbows. Look at his Abu Dhabi peformences from like what 2001 im sure hes 10 times better now.
Both Lyoto and Anderson Silva could use their footwork to keep Couture at a distance and pick him apart with deadly accurate strikes. Conversely, if Randy could fight his way into clinching range - he could work his takedowns, throws, and dirty boxing to batter his way to a decision or TKO.