You should probably mention how much DPS you are doing. If you are under performing, then I agree with them letting you go if you are not willing to improve yourself. There are a lot of things to consider. Are you doing your rotation correctly? Is there a DRG in your party? How often are you using MP/TP regens? Please elaborate on the situation.

In AS3, if you are lacking and not improving, you are going to suffer under it's intense DPS checks. MCH is not the easiest job to play, but no where near being the hardest either.