King Gizzard. They love weird-ass time signatures (look up the ridiculousness that is Crumbling Castle for an example), polyrhythms, unconventional tuning, and such. They hop from one genre to another, they probably have one of the highest album-to-year ratios in music (not including live and demo albums), sometimes they're serious, sometimes they're silly, sometimes they're silly-serious. The biggest blow to them however, is that nothing they make is truly a "masterpiece". It all ranges from "good" to "great" but nothing they've made is really a "masterpiece". Maybe in time they'll make a true masterpiece, but nothing yet quite qualifies imo.

The other nomination I'd make is Devin Townsend. Where King Gizzard is extremely prolific but doesn't make masterpieces, Devin Townsend takes his time and makes masterpieces. Despite its silliness, Ziltoid the Omniscient is one of the best, if not the best, metal albums, period. It's an album so good that even my parents, who don't like metal, have songs they enjoy from the album. Empath is a stunning blend of metal, electronic, prog, praise & worship/gospel,^1 and god knows what else. The man just does things and they come out amazing.

^1 Afaik Devin Townsend's not a Christian, sorry to any Christian peeps hoping for good Christian music. He just incorporated that sound into the album.