But if the end result is still fireteams stomp matchmakers, then the result is the same as raids. A poor experience. The fireteam gets no challenge and the matchmakers get stomped. Clearly that is a bad experience. We can't allow the possibility of that, so kill PvP matchmaking too. If people want to do PvP, they just need to go to the Tower and find other like-minded people to play with them or join their friends. That way, every single PvP match ever will be a well-rounded fireteam vs fireteam match.
If you had just looked up what mercenary gametypes were you could have saved yourself a post.
A mercenary gametype restricts premade groups for PVP. No advantages. There.
You can't apply such a thing to raids, not at all.