Here's how you fix the problem of 'mez-breakers'...
Let them die. Quick barrier of intelect, stand back, wait for mobs to have their ways with the 'mez-breakers' then mez it all, usually at this point it's probably just you standing with 3-5 mobs mezzed. Eventually enough deaths and watching the chanter be last standing drives home the point to assist and not AE during times when mezzing is needed. Granted some players are not used to grouping with a chanter and all it takes is polietly telling them, but for the hardheaded or unskilled...well...some good hardknocks work better.