We're at a definite disadvantage on a bike rather than inside an air-conditioned cacoon. Riding in the cool of the night and early in the morning is one tactic, but of course that puts us at risk of wild animal strikes.
I agree that overheating is underrated as a factor in crashes. One big problem is that riders from normally cooler climates have learned that taking off clothing in hot weather is the way to cool down.
The fact is, when ambient air temps rise above body temp, removing insulation results in the body abosorbing heat from the air rather than giving off heat. And, as the body gains temperature, lots of bad things happen, starting with cramps and ending with death.
Out west, with low humidity, evaporative cooling works well enough. I use both an evaporative vest and an evap neck wrap. But, as noted, in some humid location such as Virginia or Missouri, a soacked swamp cooler can't give off any water to the already saturated air, so there is little or no evaporative cooling.
There have been a few attempts to build cooling devices, including a head wrap you chill in the refrigerator, and vests you chill in icewater. The problem with those is that they soon warm up, and there is no easy way to get them cooled down again during the ride. I have yet to see any cooling garments that are practical for an all day ride in hot, humid conditions. The closest I have come is to buy a bag of ice and pack it in the front pockets of my Darien jacket. That lasts about half a tank, but can be repeated all day (at the expense of buying sacks of ice)
I have heard of jackets or vests that circulate chilled water, but I haven't seen any in person. It would be necessary to have some sort of onboard water chiller, and of course that would compete for space and electrical power. One summer I built a cooling water gadget composed of a reservoir and a windshield washer pump. A handlebar-mounted switch powered the pump, which s prayed water onto my neck cooler. It worked, but the complexity of the reservoir, power plug, switch cord, and water line was way too much bulk. It was just a PITA.
Maybe the smart tactic is to make short trips in the early morning in your local area when it's hot and humid--and to keep a bike somewhere else in a cooler climate for longer trips, say Seattle, Denver, or San Francisco. Yes, I know that runs against the grain of just getting on your bike and heading out any time you feel like it, regardless of the weather. But of course we already take the time for ATGATT, so it's not like we don't believe in gear.
Is there some sort of 12V chiller available that would fit on a motorcycle? Would it be practical to power a refrigerating device with propane from a "torch" bottle? Building a vest with tubes would be simple enough, sort of the opposite of an electric vest, or even combined with electric wires. Quick detach cooler lines to the chiller. We need some inventors here!