Without mentoring, disabling xp is the only way for friends with varying amounts of play time to be able to PvP together. Mentoring in PvP cannot be allowed, because any x number players who are insert_level_here can become a raid of x number of GROUPS that level instantaneously. So level locking is all there is left.
I would have no problem if locking xp locked ALL forms of xp, including quest, discovery, collection AND AA.
The other thing I have NO problem with about level locking, is that it allows players to max out their gear before outlevelling it. This would not be a problem if this game was not so pathetically easy or the xp curve so fast. But as it is, you outlevel your gear way too quickly to get any real satisfaction of having it (part of the "fun" of mmos is advancing your gear as well as levels etc.)
So go ahead and disable ALL xp, including AA when locked. Those who lock so they can stay the same level as their friends, and so they can get decent gear for the tier they are in can still do that.
Of course, the OP could also simply level past all those T2 level lockers in a matter of days, if he has a clue how to play this game, and then it doesn't matter then, does it? Or just race to max level where -- SHOCK -- EVERYONE IS LOCKED!