I don't think there's anything particularly pretentious about prog. It's all about excess, sure, but that's not pretentious in of itself. Quite the opposite, I think that level of exuberance is ridiculously honest and up-front.
https://sandsnowman.blogspot.com/ This kind of stuff is far, far,
far more pretentious. It's a big ol' facade, there's no directness or truth to it. You don't think "ooh yes, when he says he established a musical cosmos full of bright wonder, that's exactly how I consider his music," he's basically putting a hand between himself and the listener and saying "listen. this. this is proper art. look at all the levels that this is arty. oh this isn't just music this is more of a landscape, interpretted through a lens of sound, like looking out at the universe from the inside of a bubble: distorted, but beautiful." He's trying to justify it as something more than it is - and that, to me, is far more pompous and alienating than even the most self-indulgent progressive rock band.
Bands like Dream Theater and Yes and Symphony X are just out to make rocking songs and, if they're lucky, tell a good story as they go along. They'll sneak in little nuggets, but at the core they just write damn good music and pour all their soul into it. (If that's what you're into, anyway. Not a huge Yes fan myself.) It's what it says on the package, and they really honestly just want as many people to hop on as possible. You can see exactly what they're doing at every step. A big stonking song is just a big stonking song. Take it or leave it. They've not sampled the noise of a wagon wheel creaking and played it backwards to symbolise a regression to the victorian era. They wouldn't call themselves "emotional architects" or insist that their music be played at night, in a forest. And it sure as hell isn't a soundscape.
As music buzzwords go, I'm finding that pretentious is one of the most constantly misaimed. Prog's twisty and turny like a thriller, or a really clever cop show. Life on Mars comes to mind. Nothing pretentious, it just aims to thrill and do it in a clever and surprising way. The stuff that tries to be modern art or makes an effort to mimic high culture is the pretentious stuff. It's the musical equivalent of me walking around for five days with an HD camera strapped to my balls (it's a statement about fertility and libido, promise).