I can only report what I see, which is that in many parts of the world including where I live, it's always in the 30s, humidity levels are high, a lot of people can't afford air con, and there are no mass heat deaths.

If they don't have access to AC they run fans all the time, and they stay indoors or in the shade.

In fact in the cold months where it dips under 30 the local news always runs a story or two about the (small) wave of cold deaths. (I think usually in parts of the country where it gets down to 15-20 at night)

Today it was 35 in the afternoon and about 70% humidity. I went outside for a swim. There were probably over a million people in my city who were sitting outside all day because their jobs required it. It was a somewhat hot but otherwise completely ordinary day. If you said they're on the brink of heat death they'd say you're crazy.

It may be that people who sit in air conditioned offices in cold countries are translating that one study into some hysteria. It may be they will have the "opportunity" to learn to live in a hot climate like the rest of us, rather than die by the millions.