This is a very silly thing to be arguing about for this simple reason:
MD is different for all people, and some systems are better for some than they are for others. One person could say with absolute conviction that the combat system is better than the RP (dst) and another who views them more equally (kafuuka, I believe).
Which one is right? I would say that they are both right, just as every single person is right. Are those who say MD is an RPG right? Yes, although their wording implies something that I think they usually do not mean. MD is an RPG to those who play it like one, it is a FPS if you want to play it like that (though realistically, no one does), and it is a place to log in and look at the same picture every day if that is what you so desire.
As Tarquinus has argued in the past, the true beauty of MD comes when you integrate ALL parts of MD into one, that is the challenge it puts forth. Whether you rise to that challenge or not, in the end there is no punishment or reward besides those given intrinsically, and those should be more than enough to motivate someone to fulfill the challenge.
Grinders have a place in MD, as do RPers. So what if RPers call it an RPG... they only do so because RPing is the activity in which they participate; therefore it is no surprise that they view MD as an RPG.
Perhaps I am a fool, and MD is only one thing, one-dimensional, with one way to be played. Consider this also, if you so choose.
Awi