An extreme value is always only extreme in relation to some baseline. For temperatures it's usually a value that departs far from the local average. With WBT it can also mean values that approach the limit of what the human physiology can handle, a value that is quite universal due to us all being of the same species. The body cannot adapt beyond the limits set by thermodynamics.

Tropical and extreme aren't mutually exclusive. +30°C in Antarctica would be both tropical and extreme. Both are used where applicable. A temperature can also be extreme without being tropical. No matter what Trump thinks, he doesn't have the power to redefine (let alone erase) words.

The wet bulb temp. in a proper sauna should get quite high, I don't have exact numbers but above 70°C or so (dry temp. 90°C, relative humidity 50% would translate to a WBT of 74°C). In most contexts that would be extreme, but not here.