We have 4 cats, 3 long hairs, 1 short hair.
The longhairs all spend as much time in the south facing conservatory/lean to greenhouse as possible getting sun and heat.
Most sunny days its between 80 and 120 degrees in there even with the vents open – I cant cope with that heat. They love it and lounge about looking like roadkill. Vets say that cats can cope up to about 126 degrees before they have to take on extra water to deal with the start of panting.
The shorthaired cat hates sun and heat and either stays in the house or lies around under bushes in the shade during the day. He does his active life after dark.
I conclude from this warm weather behavior and also how they cope in winter, that long haired cats can deal with big extremes of temperature much better than shorthairs.
I suspect the additional fur acts as insulation against both cold and heat – that it takes a lot of heat for it to pass through the fur to the actual cat.
As long as they have plenty of water available at all times and a choice of indoors/long grass/bushes to lie under if too warm, they will cope with any heat better than you do and that unless your vet advises otherwise, they may get more problems if their fur is shaved.