Gap is huge.
Skill gap is bigger and the Illusionary superiority on one side of the fence means they will never get better.
The gap will remain unbridged.
I disagree - the "skill" argument is pure and total rubbish, whether any given player "chooses" to play PvP or PvE is not a clear indicator of relative skill despite what some PvPers try to push. That is not to say PvEers in general are necessarily better than PvPers but it is just sheer arrogance to assume or postulate that PvPers in general are better at combat in ED than PvEers in general. The "practice" argument is largely bull - a truly skilled player does not necessarily need practice, or at least not lots of it and choosing to play predominantly or exclusively PvE does not implicitly preclude that.
The nature of the gap is more about general attitudes and approaches to gameplay as a whole, which includes factors involving choices over builds. While I agree that the gap is likely to remain unbridged forever, the issues in play are far from simple or straightforward - at least in the general sense.
Specifically where combat balance in ED is concerned, it is not and should never be PvP focused in nature as that would almost preclude the possibility of ED fulfilling the "play it your way" tag line. Where NPCs are concerned, they are always going to be worse off against human players since in general they lack the spontaneity and adaptability of a human opponent. That is not something that is ever likely to change, and has little or nothing to do with the PvE/PvP gap either. Combat balance in ED is a highly subjective thing and varies a lot between encounters but overall it is balanced. Certainly there are cases where PvE can feel like shooting fish in a barrel but that is a largely unavoidable consequence of ED being targeted at a broad range of players with differing wants and desires.
The only real issues with combat balance (and the PvE/PvP divide) in ED are two fold: (a) expectations on the part of some players (both PvE and PvP); and (b) certain stacking mechanics.
FD seem to be on a path to resolving the latter of these issues, the former is something that I believe is impossible for FD to address.