People have been making the same kind of criticisms about DT material for a long time, I don't think it's anything particularly to do with the fact that it's post-Portnoy. It's just their opinion. For example to me someone lambasting elements of ITPOE or The Count Of Tuscany while praising the same elements in Octavarium, or considering SFAM god's gift to music while proclaiming SDOIT is uter crap, seems just as nonsensical to me. It is just their opinion, and while it's good to try to justify your opinion a little I tend to find that there's a very limited amount of explanation you can do before you get to a point where one person has one opinion and someone else has another. It's especially fickle when it comes to something like long term fandom of a band, since changing tastes, expectations and even nostalgia often play a role, whether we notice it or not.
As for post-Portnoy DT stuff, I think ADTOE is one of their best albums while DT12 is one of their most mediocre, but the drumming isn't really a big deciding factor for either of them.