In the past, this was because of disease caused by pre-sanitation density. Today, it is due to below-replacement fertility rates caused by impossible to afford living costs.
So if you consider extinction a form of human suffering, 'traditional walkable cities' fit the bill.
Untold millions have lived in big cities since the time of Babylon and earlier.
I don't know where you get that interpretation, but most historians will say that is exactly the opposite reason why cities were developed. Historically, people moved to cities so that they would NOT die.
Living in a city amongst other people provides one with a greater defense against roving bandits and others who want to kill you and take your property/food. That is how cities came into existence. There is also the benefits of trade. With trade came specialization so that not everyone had to be a farmer to sustain themselves. One could become an artisan, a priest, or a warrior.
(I'm honestly not sure if this is a troll comment or not. I'm going to give it the benefit of the doubt though.)
Alternatively one could say any cursory reading of history will reveal that cities are and always have been where humans go to prosper and innovate.
Also, and more importantly, the majority of dense, walkable cities do not have high costs of living - e.g. Berlin, Barcelona, Istanbul, or even much of Chicago. Just because the most expensive major global cities are dense and walkable that does not mean that all dense and walkable cities are expensive.
If you look at the most expensive zip codes in the US [1] you'll see that eight out of ten are in low-density suburban or semi-rural areas. Does that mean that low-density suburban areas are all super expensive?
[1] - https://www.forbes.com/sites/betsyschiffman/2015/11/10/full-...