PvP gear in PvE is just as good as PvE gear in PvP.... and by that I mean they both are much weaker then the appropriate equivalent.
You should immediately assume that anyone who is doing this is basically the weak link in the group comp (unless another member is clearly under geared to the content itself).
I'd rather someone brought Battlemaster than lvl49s. In many cases, a Battlemaster piece is significantly better than the equivalent Columni. I've often hit 50 with 3.5k ranked WZ comms, and 2k normal comms, and moved into nearly full Battlemaster. Storymode operations are definitely do-able in that condition.
Also, many, many theorycrafters argue that BIS relic for almost every class is the Warhero Relic of Boundless Ages (situationally slightly less attractive than matrix cube). As far as I know, there is nothing better.
The reason PvE gear is such a huge disadvantage in PvP is expertise: there's no equivalent for PvE. Yes, your stats are slightly lower than equivalent tier PvE equipment (often most pronounced in terms of HP), but you're not doing a solid 30% less damage or taking a solid 30% more damage.
In my experience, severely undergeared players who know what they're doing can perform very well in PvE content. Even a very good PvPer with zero expertise is going to have an extremely hard time in Wzs.