Look at pot pvp in 1.8, you have to manage your health and not die really fast. Ok, look at 1.9 pot pvp, all you have to do is take it slow, and it's impossible for people to die very fast because they don't forget to pot themselves unlike 1.8.
Edit: 1.8 requires more health management.
1.8 in ffa is broken because of the knock back, not just that, also the hit registers is broken too, ask 1.8 pot pvpers to go there and try it, they will say the same thing.
Problem is that if we keep both, eventually players from 1.8 are gonna want stuff that are from the 1.9 updates, what will cc do there, that's my question