Are novel cover blurbs too hyped and "breathless"?

I am not sure if this is true across other genres, but in the crime/thriller/adventure genres it seems common for fiction novels to have book-jacket blurbs along the lines of,* “An expeditionary team discovers a terrible secret in the Arctic that will change the future of humanity forever! A vast conspiracy unlike anything the world has ever known! Follow our heroes as they race against time to prevent doomsday.”
*

These blurbs aren’t being written by the authors themselves, right - by the publishers? And are they having the same effect as clickbait of the “You Won’t Believe What Happens Next; Click To See Now” variety? Especially if what’s in the novel is a disappointment compared to the breathless hype of the blurb?

Wouldn’t a more…restrained synopsis-blurb be better?

They’re written by the marketing department, which thinks that sort of blurb gets readers to buy the book. I don’t know if there’s any actual data to back it up, but that’s been the way things have been since books first had blurbs.

There are some books with more restrained blurbs – usually literary novels and, of course, nonfiction. But the audience for literary novels is believed to balk at clickbait type blurbs.

If the blurb makes readers pick up the novel and buy it, how exactly does the publisher not benefit? Do you honestly think that a less-effusive blurb would sell more books, or even as many? Do you honestly think that if the book was a disappointment, the buyer will blame the blurb writer instead of the author? Publishers have every incentive to do this and no disincentive. I can’t understand your issue in any way.

Same with exaggerated cover art.

(Although not always. Tolkien’s own watercolors for Lord of the Rings were very subdued.)

Not sure about that, the box full of airport lounge level of books a friend of the family dropped on us once was replete with Nazis, explosions, helicopters, Nazis, jet fighters at crazy angles, more Nazis and the stories inside really did deliver all that.

"[This worthless piece of shit is] by the author of the [overhyped] best seller . . . "