*Obligatory Dragonite/Rayquaza are best available current options* response
i dont see any need ot TM away or buy a new charge move for DM, its a fine move, if you're going for absolute best speed run record, then yes thats what you should do, but otherwise i dont see much reason to get rid of it.
Just as i recall you mentioning to me a while back when i was contemplating something similar, they are very close in preformance, and sentimentality/novelty is a lot more important than a nearly unnoticeable preformance difference.
Its a very powerful move, its why i kept DM on my 96% dragonite i got on the first CD, my first great pokemon that i ever caught in the game. Just maxed it out today after being level 34 for a long time