Cheap tires are slower. Reliable tires are slower. It's obvious from the pictures that the fatties they're testing are special, with paper thin skinwalls. I can totally see that a high performance fattie would be just as good as a high performance narrow tire. It's the inelastic deformation of the tire casing (and inner tube) that eats power.
Unfortunately thin-walled high performance tires are also delicate. I've seen people ride tires that can't even survive a couple of kilometers of dirt road.
The Rene Herse tires are just branding on tires he has made for him by Panaracer. They used to be called Compass Tires till he made a deal with the Rene Herse estate to use the Herse name for branding.
He basically asks Panaracer to make everything thinner & lighter and delete flat protection, reduce the tread thickness, etc.. They are fast & potentially comfortable tires for their size due to being made as very racy tires. The Panaracer versions of the tires are still very fast but have a much better reputation for durability, flat protection, compatibility with a wider array of rims, and for being easier to setup tubeless.
I have unfortunately been on rides with people with the Compass/Rene Herse tires where they repeatedly flatted over and over, IMO they are too fragile for me. I have had exceptionally good luck with the Panaracer tires.
Yet, some high profile riders such as Ted King (possible the top gravel racer) and Lael Wilcox (ultra endurance racing and bikepacking) use these tires with success. If someone is getting a lot of flats using the Extralight casing, they should consider the Endurance or Ultra Endurance casings and/or setting up tubeless.
But even Jan will recommend the Panaracer Gravelkings when necessary, especially off-road[0].
Those riders are all influencers and likely getting the tires through sponsorship though, that is something that always needs to be kept in mind with cycling. They don't make enough money to necessarily be able to ride what they think is best if something else can be ridden for free or for payment.
These people are routinely winning long distance races on offroad and unpaved surfaces using these tires. That is evidence that the tires are indeed durable, regardless of whether they would prefer other tires.
I’ve ridden their extra lights into some pretty ridiculous places, and commuted on them in a city, and they’re as trouble free as any other tire I’ve had. (In about 7k miles)
I would recommend taking them on technical single track, but they rock for any sort of road riding. They’re certainly fine for the gravel I’ve seen.
(And by trouble free, I mean no flats that I can blame on the tire or some damage to it. I’ve had one slow leaky valve that I had to change on a ride. I’d normally get a flat every 1-2 thousand miles or so with my older tires)
The real test for a city is how many hypodermic needles and smashed bottles can you ride over before being stranded by a puncture in a not-so-nice area of town at night...
My old narrow tires would tend to collect cuts in the tread, sidewall cuts, and other damage. After a thousand miles or so, I’d tend to be able to see the cords in some of the cuts, and I’d occasionally dig bits of glass or stone out of the rubber.
I just don’t see the same sort of damage after 3500 miles on a pair of 650x42 tires. I’m not generally riding over needles or goat heads, and I avoid broken glass as much as possible.
I’ve been commuting on the extra light Rene Herse tires for about a year in the city and haven’t had a flat. They are set up tubeless though. They are a joy to ride and greatly improved the speed,
comfort, and handling of the bike. I was hesitant to get them because most of my riding is on city roads with debree, but haven’t regretted them at all.
The problem I’ve experienced with these expensive tires (compass, gran bois, etc) isn’t their durability against road debris. It’s that their “supple” sidewalls don’t hold up to the equatorial sun I suffer under. They degrade far faster than the tire rubber degrades. I like riding these tires but they are expensive fast consumables.
Unfortunately thin-walled high performance tires are also delicate. I've seen people ride tires that can't even survive a couple of kilometers of dirt road.