The shower is higher humidity though, and the hot water makes direct contact, so the heat is more conductive. Similar for a steam sauna, they are more potent at the same temperature. Also infrared saunas, but for a different reason (the light is absorbed directly into the tissue, without needing to heat the air). So it's definitely not just about temperature.

I can definitely turn my shower up for a hotter body experience than any sauna I've ever been in, and obviously it's nowhere near 150-195 which would be lethal.

Because the water is making direct contact with my body for much more heat transfer. The dry air of a sauna is vastly slower, plus you're sweating which provides evaporative cooling which isn't happening in the shower.

So I too really don't see how saunas are appreciably different from hot showers here.

A better question would be the effect on body temperature. Obviously, water transmits heat better than air

i imagine hot shower also worse for your skin