It seems they adopted a uniform setlist for this tour because their schedule is so tight there's just no room for rehearsals. They have to perform like 5 venues in Japan alone.
These Dreamtheater guys are a beast they are in their 50s but are so active. I don't think I can handle that kind of schedule I will break.
DT's had exclusively uniform setlists since 2014. They have also employed a great deal of digital assistance (metronomes, pre-recorded backing tracks) since then.
Also, there's nothing unusually strenuous about playing 5 shows in Japan. Japan is big. They should have spaced out the shows more in terms of time (LaBrie is not doing well), but there's no other reason for this tour to be harder on them than any recent tour.
Anyways, after MM joined, there was a small amount of setlist variation, but not much. There was a bit less after the 2011 European leg, and then none by 2014. It has nothing to do with the difficulty of their tour.