The act of MTing isn't hard in any way, the fact that DRKs take considerably less damage than PLDs do on the tankbuster in A4 make them the better MT for that situation.

Just because you don't want to learn/play more than 1 class doesn't make this any less true.

There's a difference between being good at MTing (knowing the fight, holding agro and maximizing self dps while staying alive) and being a good MT. You can be good at MTing and still cause extra stress on your group from your lack of desire to play/learn another class to help in certain situations.