Wet Bulb alone is not sufficient

The latest widely cited paper on human limits does NOT endorse the wet bulb temperature as accurately mapping human limits.

Quite the opposite.

A lowered wet bulb threshold of around 30C (86F) is suitable for assessing high wet bulb temperatures that are mostly from high humidity below dry bulb temperatures of 40C.  Above 40C (104F), the wet bulb temperature does not adequately assess the stress from dry heat alone.  At 50C (122F) the critical wet bulb temperature has fallen by 4C to 26C.

It still looks like the wet bulb temperature limits, with these caveats, are good to 50C dry bulb, and predict these limits better than other measures.

Meanwhile, I'm continuing to make no sense of the heat index in these regards.  The heat index can also be calculated by temperature and humidity, but the result does not highlight the danger of very high humidity at relatively low temperatures in the same way that wet bulb temperature does.  Comparing a few calculations, it appears to me the heat index underplays humidity at low temperatures, and overplays relatively high temperature and low humidities, as compared to the wet bulb temperature, and probably human limits as well.  

For example, the Heat Index of the now accepted threshold for wet bulb temperature in humid environments (30C at 100% humidity) is merely 112F.  Holding the wet bulb temperature constant but raising the dry bulb temperature to 40C where wet bulb is still a useful measure (40C at 46% humidity) yields a heat index of 126F.  Adaptability is about the same but the Heat Index has shot up by 14F.  The heat index at the formerly believed wet bulb threshold temperature (35C at 100% humidity) has a staggering Heat Index of 161F.

The heat index is only useful because it more intuitively maps higher than average humidity levels into elevated temperatures.  Without a full explanation, and possibly some un-learning, people lacking scientific backgrounds may find it hard to fully understand the wet bulb temperature criterion (I myself have had great frustration trying to explain it to people with more verbal than quantitative backgrounds) because the threshold numbers just seem too low.  But you can't just add 20C to the wet bulb temperature to get the heat index, they are based on different functions.