Not really sure how much further they could push it and not go into some kind of mathmetal or neo prog metal

LTE for example. I think they pushed and reached the limits of prog metal...before it's something else post-prog.
After years of pushing speed in thrash Metallica and Megadeth, etc., also dialed it back
Technically and musically Rudess is lightyears beyond Moore, and any other keyboardists they had. Mangini is a technical machine also beyond Portnoy.
Now with Portnoy back, I think they're in re-adjustment mode with Parasomnia, and we're going to see future DT dial it back, maybe more melodic explorations again.