I have written in the past that PvE and PvP should not mix in an MMO. That argument is based on the player desires and the shifting between the two gameplay modes. However recently I realized there might also be a mechanical difference between the two modes as well. Note, for this discussion I will be calling MMOs where the majority of the player’s time being spend fighting computer opponents as PvE regardless of their PvP offerings.
In the majority of PvE MMOs what provides the majority of complexity and depth to combat is the large number of abilities the player’s character is granted over the course of the game. Look at any screenshot for WoW, LotRO & Rift and you’ll see at least two bottom bars and a couple of side bars chock full of abilities. I have played each and found the PvE experience infinitely more satisfying that the PvP experience.
Now, look at similar, successful, large-scale games which are designed for PvP in mind. Guild Wars, League of Legends come to mind. How many abilities do GW characters have? 10. How many abilities do LoL Champions have? 4. Granted, neither of those are MMOs in the traditional sense but the pattern holds. In EVE most ships have a handful of slots to use. those with a large number of slots often group like modules together so you end up having a total number of powers numbering less than 10.
It seems that PvP and PvE have a systematic difference to one another. The more satisfying PvP experiences have fewer player abilities and derive their complexity through other means. The more satisfying PvE experiences have more player abilities and derive their complexity through the use of those abilities. If this is the case then it might be an objective basis upon which a case on keeping the two separate could be made.