I've heard that these abilities are PvE only from some people, but then others are saying they are RvR only, which is it?

Neither, really. MAs are designed primarily for use in RvR. Some of them will only be usable on "realm enemies" meaning enemy players, enemy guards, enemy summoned pets, enemy charmed pets, etc, but not on NPC monsters. Others will be usable in both PvE and RvR.

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