My boss shaves Great Pyrenees

Goodness! Former groomer & have owned many pyrs. I've had legitimate working pyrs, others that were only outside pets, some indoor/outdoor, & some coach potatos that could care less about the outdoors. I live in your same region.

They need their double fur coat in order to maintain their core temp. That double fur layer creates a pocket of air insulation & is their main method to regulate themselves. That includes in 115 degree weather with extreme humidity. They need both layers of fur for the extreme heat & cold.

Part of the reason pyrs shed so much during hot seasonal changes isn't because their fur is so long. The primary coat that sheds like crazy is the undercoat. It thins itself out underneath for summer. Losing that thick downy layer keeps them from holding in so much heat. The overcoat stays long to trap in cool air. Imagine pulling most of the stuffing (undercoat) out of a your heavy winter jacket. There's only a bit of stuffing & the jacket shell (overcoat/guardhair) left to wear. You won't be hot anymore, but there's still a safety barrier between you & the elements. The overcoat does all the waterproofing & provides sun protection. Plus the bright white to cream fur color reflects sun instead of getting hot to the touch (so it doesn't add body heat).

In winter the undercoat gets very thick to hold the heat to their bodies. The overcoat holds even more in. (Imagine how layering socks of different thickness/density helps in winter). The overcoat is still doing it's waterproofing thing for snow & slush; so, their body isn't actually getting wet. It's why people can pet them & they'll be wet on top but dry underneath the fur layers.

A pyr shouldn't ever be shaved unless there's some major skin issue or matting that can't be addressed by a better method.

Owners who are knowledgeable about the breed will never take them to be shaved. Part of being a groomer is educating clients & refusing service when the service is harmful to the animal. They can, of course, be given baths or have their fur shorten/evened out. Shortening their fur isn't necessary, but it can make things easier when caring for a primarily indoor dog. Indoor pyrs normally need some booty hole trimming and paw pads defuzzed. When shortening the overall body, they should never be cut into the undercoat & some length needs to stay overall.

You're correct about the fur not growing back properly. Sometime the dog gets lucky & it eventually turns out fine. Most of the time it's causing a bigger mess. What you described on the fur is actually the poor pooches getting sunburnt, bc they don't have the guard hairs to protect them. Their skin is usually naturally pink or very white. So like pale AF people, they're going to fry if it's not covered. Shaving also makes them more likely to develop grass & skin allergies. The overcoat will get tangles, burrs, and grass seed, but it also helps to hold irritants away from their skin and body. If you pay attention, an unshaved pyr in extreme hot temperatures either won't be panting like crazy at all or as bad as a shaved pyr.

Your boss really concerns me. Pyrs aren't the only double coated dogs and the no shaving thing applies to other breeds too. Sorry about my rant. Basically I don't believe in shaving them as a groomer or an owner.