Portnoy is easily, hands down the best thing about DT. Unfortunately I don't think he's good enough to save them, either. I don't rate his technique, but what really bugs me about him dawned on me earlier: it's all tab drumming. Tab drumming? What the hell does that mean? Rhetorical questions aside, I just think his drumming all sounds like the kind of stuff you would design to write out in tab form: it has no serious amount of dynamics, no changing articulations on each surface, and most importantly it's all aligned to a metronomic grid in time and each note is only about its attack - there's no consideration of sustain, tone or space between notes.
If you listen to, say, Brazillian music you'll hear various things at work. One common phrase used is commonly written as a 1e(+)a phrase (where the "and" is not played) in 16ths, but which is actually played closer to a mix of 16th notes and triplets. It has a really nice feel and shape, and while it can be mathematically described it doesn't fit exactly into either a triplet or 16th note conception. You can't really tab this stuff accurately. It also has a lot of dynamics and articulation, and there are things like note lengths coming into play.
For me this difference between dynamic, articulated drumming with fluid, engaging time and the metronomic plodding stuff you hear from Portnoy is like the difference between a website designed using tables (i.e: lots of right angles everywhere) and a painting on canvass. One has been jazzed up to the best of the ability of the artist working inside serious restrictive logical requirements, the other is total freedom and a lot more human and expressive.
If you insist on playing everything as attacks written on a grid then there aren't a lot of ways to make that interesting - changing the dimensions of the grid is almost the only one, which is why Portnoy plays so much stuff in varied time signatures in DT. But really changing the dimensions of a grid doesn't make the stuff you build on that grid any less square and uninteresting, at least not for me.
As for bands with similar degrees of complexity to DT... there are many. I'd argue that Secret Chiefs 3 (just for one) is considerably MORE complex, but it's a very different kind of music so we'll ignore that. Staying inside the whole heavy/progressive/technical realm I'd have to just point to Fredrik Thordendal's solo album again, and Morgen Agren's loose, funky, fluid drumming over the complexity in that particular environment. That's NOT tab drumming...