Dream Theater have been all over the map. Or, maybe, I should say Dream Theater used to be all over the map. I think it's unfair to judge DT simply based on their most recent output, but I can how SC and BC&SL would make one think that they're primarily a metal band.
I have a feeling Kev's been a DT fan long enough he doesn't judge them just by current output
And now, just because, I'm going to break down each band's album stylistically:
DT
1. WDADU-80s style prog with a bit of Maiden and Rush
2. Images-Epic sounds, progressive metal.
3. Awake-BALLSBALLSBALLS less prog
4. Falling Into Infinity-More of a rock album than anything.
5. Scenes-Their most "rocking" album to date, with more prog than metal
6. 6DoiT-Super Prog
7. Train of Thought-Super Metal/Technicality
8. Octavairum-More prog pop than anything, but tracks 5-7 bring some heaviness
9. Systematic Chaos-Prog Metal with monsters. BALLS
10. Black Clouds-Epic prog metal
PT
1. OtSoL-Psychedelic
2. UtD-Psychedelic
3. TSMS-Pink Floyd-style psychedelic prog
4. Signify-Moving on to something heavier, exploring more pop elements
5. Stupid Dream-Pop elements but still clinging on to some psychedelic weirdness
6. Lightbulb Sun-Probably the closest to a pop album, but features their first blatant prog song.
7. In Absentia-Metal, with some pop and atmosphere thrown in.
8. Deadwing-A combination of LBS and IA's styles
9. FOABP-Heaviest to date, most prog-sounding too.
10. TI-Still pretty heavy but totally different from Fear's style.
Just from doing that, I couldn't really find myself describing DT's music outside of "rock, prog, metal" while PT's has gone through so many phases that usually wouldn't be caught in the same room together. While DT has explored different styles, they've always stayed in their niche, while PT, especially early on, has just sort of gone for it and it just magically sounds perfect for them.