Well the problem with a dark magician based deck is the speed and consistency. The deck is just not fast enough with high level magicians even with all the support often times you wont draw into what you need. As for the consistency there is too much the deck CAN do, there is so much support for dark magician that often times you try to overload it with support and cant get out enough monsters. A hand full of spell and trap that supports a monster that you cant even get on the field is no good. Also there is DMG, I love her don't get me wrong but its just not worth it, the main focus of a Dark magician deck is to get him on the field and defeat them with alot of attack (cough but 2500 is not alot now days) Most of the time you are at the most going to have only 2 dark magicians in play (hand, field, or grave) at a time. As for the ritual magician, well hes not even worth it, relinquished is a better option then he is.
Overall a much better deck is a spellcaster deck with the magicians spliced into it.