Is there even actual evidence that Ninja is not best in PVP? I think not, it's all just a matter of opinion. I never have issues taking down Monks and dragoons in PVP ever, only real times i die to them is if a few of them gang up on me.
And yes i am nowhere near top player in PVP so either other melee are always just bad or just maybe Ninja is actually good in PVP .....