The wierd thing is that Dante's DT never was the same design. It was never inconsistent.
They never mentioned his power has grown or he trained and never had a great effect on the story.
(Except for Nero that is)
Which is damn strange for a game that has a half-human morphing into a full-demon.
In DMC3 Dante only changed into DT for about more than one-second but less than three.
In DMC4 he changed while being hit by nero like a dimming light bulb.
But I must admit DMC2's DT is the BEST.
Just look at it, Ebony and Ivory is now bloody Dual Gatling guns. And Rebelion is set on his arm like a spike. Also we know it is Dante because the demon form has white hair as well. Pity the game itself was a flop...
Yeah, The DT has been intriguing. I am gonna talk in DMC 3 and 4's terms. DT seemed as a sub-conscious response when dante was in danger or forced to the point of death or a state that will make him unconscious. Ofcourse, in gameplay terms DT is really powerful when completely upgraded(by charging it up) in DMC 3. And with distortion effect in DMC 4.
This brings me to intriguing myth of Sparda. Sparda did not put an END to the demon world. He jus found a way to seal the demon world from causing any harm to the human world. And who knows how much it took out of him to accomplish that. Yeah, he did a good job and his DT is commendable as a powerful weapon but to me, it could only be used by those that understood its purpose.(like using it as a defensive tool than an offensive weapon).