... (i don't think i) could say how it 'ought to be' ...
Sure you could. It's all opinion. Aaaaall of it. :-)
Except it's not really, because it's rooted in selfishness and delusion. THEY are the artists. It's THEIR statement. They are just as "great" as they always were. It's not like the all of a sudden forgot how to play their instruments, or forgot how to play together. It just doesn't resonate with YOU. That's not really "opinion", it's just the fact of what you like and don't like. There might be "facets" of their current choices you don't like, but it is arrogant in the extreme to say that because you - one person out of 7.3 billion people on the planet - don't like it as much as something that came before that therefore they are "[no longer] amazing".
"Images and Words" is a top ten album for me, all time by any band. Octavarium is close to that, as is Six Degrees.... I am not on the train of the "Mangini era". I think he overplays at almost every opportunity. I think the greatest of rock drummers - Peart, Bonham, Collins, Portnoy - make playing in "19/16 time" sound like "4/4" even if it isn't (think: "Turn It On Again"). Mangini has a way of making 4/4 sound like 19/16, and that's not a compliment. But that's on ME, not the band. They made their choice, they are clearly happy and inspired (by any analysis, "The Astonishing" is an inspired work, even if it hasn't resonated with each and every individual fan).