The over-reliance on their current metal sound as of late is the issue I have. They obviously still have diverse things going on still within their albums. They transcended genre so much in the past, that it's hard to see that DT, a band of virtuosos who know how to write music well, have become a bit "formulaic"
I will grant that most of the modern albums are less eclectic than something like I&W, FII or SDoIT. However, this sort of expand-contract musical evolution of stylistic diversity I think is probably more common than you'd imagine. It's a process of establishing their sound, exploring its limits, establishing a balance and a new stylistic centre, then refining that to suit what they want to achieve musically. This cycle has happened with bands like Rush, Metallica, Black Sabbath, Queensryche, Deep Purple etc. They also may very well simply feel like the songs they write are generally less malleable to eclectic experimentation and highly contrasting styles. This of course doesn't stop stuff like the raw jazz fusion style solos in S2N and StR, the exotic piano comping in UA and LNF, the funky guitar interlude in BAI, the jazzy piano flourish or the entire orchestral section in IT, the Morricone esque build in FItL or... just TA in general. The fact that these often don't feel like heavily contrasting moments is probably a testament to how smoothly they're integrated into the sound.
TOT is an interesting one to bring up, as the reason it was so controversial at the time of its release is because it was the first DT album where (pretty much) all the songs were metal, meaning that wasn't a thing before. Leading up to that they had a few tracks that were heavier than their usual fare, but it didn't dominate the album. TOT was cool because it was something different than before, and the style of metal they did there is different than what they did after. Later albums don't really have that groove, nu-metal, and angst-filled riffage of TOT; later stuff is darker, with more chugga chugga riffs. After Octavarium, their sound evolved into incorporating a certain metal tone in the overall sound and mood of the album. As I said, for all its lighter moments, The Astonishing is included in this debate.
I mean, the heavier moments (at least in large part) on TA are arguably more textural than anything else, so I really don't know if it can be included. Only about 5-7 of its 34 tracks would kind of fit the bill. Is simply having that modern metal sound enough to draw ire? I also don't know if I'd call most of the riffing in these albums otherwise all that dark. Stuff like The Enemy Inside, Untethered Angel, My Last Farewell, Room 137 and Paralysed, sure. Fall Into the Light, S2N, The Looking Glass, Moment of Betrayal and Behind the Veil (again, in spite of the tuning, it's got that early 90s Megadeth esque groove) I'm less sure about. In my view, 4/9 songs on DT12 fit your description and 5/9 from D/T. I'd hardly call that overwhelming, even if the latter is the majority.
(Yes, last 2 songs on BC&SL tone down the metal as well, but the previous 4 tracks were all just heavy af (or a metal ballad))
Neglecting to mention that those two songs total over half an hour in length. I also think including Wither as a
metal ballad is... a bit of a stretch, not to mention that the Beautiful Agony part of ANtR is such a prominent part of the track (it's pretty much a full song within a song) that I feel like it also merits inclusion in the overall balance. As for the rest of the paragraph, I guess that is a matter of opinion. The thing is, I don't view the MM era as going for the same kind of thing in this regard, generally more going for a sort of layered, dramatic vibe (hence why a lot of it is textured with melodic keyboard parts) over visceral sonic impact when it comes to a lot of these metallic sections. Constant Motion might hit harder than The Enemy Inside on balance, but the latter feels more tragic. I personally quite like both approaches, with the respective drummers suiting each tone.