The main difference is that the way PVE is designed is to become gradually easier over time (in DS case it became substantionally easier over time). PVP does not since as you gear so does the competition. But anyone saying PVE is "easy" is not a top tier raider and doesnt understand it. Sure you might be able to get into a guild now and do DS like wow what a joke, even if you are absolutely pathetic its easy to carry many players through it. But when fights are new without nerfs and players lack most raid gear the amount of skill and coordination required is immense. Even when its nerfed getting high world rankings is very skillful in many cases, which in a way is an element of PVP in a PVE environment as those ranks are going against all the other players in the world and not the encounters. And this idea that PVE encounters lack variables is also absurd.
On the main topic if the PVE weapons end up SLIGHTLY more powerful in dps terms than the PVP ones I dont find that a big issue since the PVP ones naturally have a lot more survivability. If the PVE weapons are VASTLY more powerful than thats a problem as it forces PVP focsed players to do something non PVP related in order to remain competitive.
Oh and just a quick side note. Throughout BC I was a feral tank and many times the PVP gear was actually BiS for tanking forcing ferals to PVP in order to be as geared as possible. So there has been times where PVE players had to PVP as well. Not saying it happens often but its happened!