As for discipline. I believe that if we have 70-80 disc we can keep up with legacy nats. I've done 1v1 yesterday with my friend and tested it out. We did not shoot and I wanted to see how much disc I would need to keep up. By the time I ran out of disc I used preparation and then continued on. By the time i ran out again my prep was ready again. But I would say legacy should have a little boost over new nats but not by much. The reason is because I would use up my backup plan which is 60% health gain while he still has that as a backup. In a real fight once i use up my prep im vulnerable while the legacy nats still has it available.
I tell you this though. legacy nats will not save you if you are a glass canon such as my friend. i think it was 20-0. Well the other factor is that he only had 80k dps with sharpshooter. lol.