Temperature usually fluctuates between 45-50 in peak summer days. That is the time when you cannot do much outside, but people do work. Most people have air coolers or air-conditioners at home and work.

Nights are relatively cooler, but heat waves can continue till late night as well.

I recall from my trip in 2008, doing camel safari from Jaisalmer (west india, Thar desert, amazing place). I counted plastic bottles and drank 6 litres of water just on the camel, and literally nothing came out of me. Sweat quickly evaporated in that low humidity environment. It was around 45-50 degrees outside, just sitting on that animal, slowly moving around.

At one point, I nearly collapsed from heat fatigue. It was just a sudden weakness, my head spinned a bit, I had to sit down and after few minutes I was a bit better. This was 3rd month backpacking in india, so one would expect at least slight adjustment. In cities, you just move from one AC place to the other and suffer through short periods outside of it (in fact heat subjectively gets much worse if you stay predominantly in AC place).

I can't imagine people doing any physical work under these conditions. There are some hard limits on human biology