Heat Indexes and Wind Chill are real numbers that represent equivalent dry and still temperatures for the same amount of time to have actual damage to your body.
I have been in actual temperatures ranging from 127°F down to -48°F.
I was once in an actual temp of -35°F and enough wind to make it -72°F. I speak from personal experience that the -35°F (wc -72°F) was FAR, FAR worse than the -48°F and no wind.
I was working in Homa one summer re-rigging a heavy lift barge.
The sun beating down on the steel deck made the temp inside the barge over 130. we weren't supposed to stay below deck for more than 45min.
The temp difference between below deck and on deck in the shade was so different you actually felt cold you would have to stand in the sun until you cooled off.
Every afternoon it would rain for about 30min. The deck would cool so quick water would condense on the ceiling and it would rain inside the barge. Felt like someone poured ice water down your back.