They are seen as challenging side-content. They don't reward you with anything but cosmetic stuff and a sense of achievement, so they're not part of progression. They are definitely a challenge, especially when done timed. Getting a gold rank requires solid communication, planning, and playing skill. Probably more so than any 5 man content ever before in WoW.
It's less prestigious than heroic raiding I'd say, but if someone has the full transmog set I definitely know he could play this game on a high level.