^I think that's a fair way of looking at it. Whether that is what MP and MM intended, I'm not sure. But I think that is certainly how it comes across to the listener.
Portnoy's up-front, "lead" style of playing really shines through when he is playing prog., as in DT, Transatlantic, and Neal Morse. But he shows he can also play more of the backseat role when playing more straightforward material, such as in his covers projects, on cover songs he has done with the three bands above, and even in more straightforward metal bands like Avenged and Adrenaline Mob.
Mangini, on the other hand, often seems to be a lot more subtle in his playing so that even when he is doing something amazing, it's not as in your face, so it is easy to miss if you aren't paying attention to what he is doing. And the times he does want something huge and in your face, there is a more pronounced difference in dynamics that calls your attention to it.
If you are a fan of insane drumming, it's a great time to be a DT fan, IMO. We have ten mindblowing albums from Mike Portnoy. And a new album and potentially long, productive future of completely different mindblowing albums from Mangini.