Perhaps a difficult question. Is DT's popularity worldwide on a downward curve. Of course there are several good new progmetal bands that they have to compete against, but it seems like it :-
Surprisingly few tickets sold although it is a bit early on the Europe tour which starts in jan 2020
Difficult to answer without some really detailed supporting information. But in a nutshell, they are more staying level, if I had to really choose. But popularity ebbs and flows, particularly for a band like Dream Theater. The competition nowadays is high, but it has always been high. DT is a niche band, in a niche genre, who needs crossover appeal to some mainstream hard rock and metal fans to really expand the fan base. For the most part, they have achieved that. And generally speaking, you've seen young fans at DT shows -- and not just kid that parents brought along. These are your late-teens, early-20-somethings going on their own and being fans.
That said, however, I really do think the band shot itself in the foot with The Astonishing. I'm not talking about the merits of the record artistically. I'm just talking about how polarizing it was. On one hand, you applaud DT for sticking to it, and performing it in its entirety. Relevant bands support their new music. On the other hand, it was a stretch for those more casual fans (a group I consider myself a part of, even though I've been a fan since the mid-90s), because the album's eclectic nature really soured some people.
Using myself as an example, after buying The Astonishing, trying hard to get into it, and ultimately just not liking it, I passed on seeing the tour (which passed through my area twice). The record, if we're being honest, was this era's Falling Into Infinity -- it has its fans, but many do not like it. And so DT played "recovery" by doing the I&W anniversary tour. And now, the DoT/SFAM tour does the same thing -- pairing new stuff, but having a classic record to bring those mainstream people into the fold.
For me personally, I love DOT, so I would have gone regardless, but I wouldn't underestimate the fans that would not have gone to see DT had SFAM not been played. It's a selling point, and a smart one, given what happened with The Astonishing.
I think Dream Theater has rebounded from The Astonishing (again, not talking about the merits of it artistically, just in terms of its impact on the fan base) quite well, but I don't think the band is "on the rise." They are treading water successfully, as they generally always do, with some good will from a well received Distance Over Time album. The venues have varied, but for the most part, they are slightly bigger, which is a good sign. But I just don't see them continuing to add fans by any sort of wide margin. They're staying afloat
Again, as always, just my opinion.