Well, it's not always that simple. One technique can be correct at a certain level but at a higher it's not good enough. There arevery few techniques that a good instructor can't counter.
Right. Point is, if YOU cannot counter or ignore it, YOU are not currently qualified to deem it incorrect. This is far more valuable information than the achievements of your predecessors.
...If the intention of on-mat student-to-student teaching is to help and improve, I think that it can be very beneficial (even if their comments are "wrong," if said with good intention, it is much less irritating than if they had said it to prove that they were smart), but there are "helpful" students who are just trying to feed their ego.
If you want to learn how to deal with uncooperative and selfish people, you must practice with those people. Or with people playing that role sincerely.