So that 10C difference only feels like 2C difference, but comes with the complications of being all sticky, which might make you feel more miserable overall despite being technically cooler.
Also, I don't know enough about wet bulb, but would it be possible that if humidity is higher, that sweat evaporates more slowly, and accumulates rather than just evaporating? If sweat drips off your body rather than evaporating off, do you still get the cooling effect (is it the releasing of sweat, or the evaporating that cools you?). Walking through a park on a summer day and a lab environment are going to be a bit different.
Basically, my question is, does wet bulb temperature accurately represent the human body, or is this a spherical cow moment?
Less evaporation happening is exactly the mechanism by which the wet bulb temperature is higher the more humidity there is. Sweat dripping off doesn't invalidate the model because heat is still being pulled away at the maximum rate, it's just that the body is expressing more moisture than actually needed.
I was more thinking of things like surface area. At a certain point, once the sweat starts pooling, the sweat to evaporation ratio goes down (since it can only evaporate at the surface, which is further away from the skin, so now sweat is also insulating).
And the point of evaporative cooling isn't that sweat is taking heat away from the body through contact heat transfer. Evaporation actually uses heat for the phase change, which means that a single drop of sweat will pull heat out of your body through standard heat transfer. And if it drips. then it has just pulled that heat away. If it evaporates, it will actively pull even more heat away. Which is why wet-bulb temps can be below ambient. If the sweat drips, you don't get the evaporation benefits. So if you sweat to the point that you are dripping, I would have to believe that you wouldn't hit the ideal wet-bulb temps, and would thus be hotter.
38C@30% humidity = 24.4C
28C@60% humidity = 22.2C