We need cities that are easily traversed by humans, not cars.
More, smaller cities - or even large cities with multiple “city centres” - and an approach which attempts to ensure that the SF centralisation of the consumer tech industry couldn’t be a thing, would be the solution, surely, if you decided to design from top-down?
In the affordable housing I've lived in, we had malls, parks, cinemas, skate parks, all within walking distance. Pedestrian bridges over any busy roads so you could take your young children everywhere they'd need to go without hopping in a car. The result of the social housing boom of the last century in the UK. Work might be somewhere else, but you'd take a bus or a train there, depending on what city you live in. It's unlikely that there'd be staff parking where you work, anyway, unless you worked at an office on the edge of town, even if you had space for a car at home.
A home to 5M people isn't likely going to be very walkable.
That's not true. One solution is the '10 Minute City/Neighborhood' and its guide to decision-making.
Also, if you have a bicycle and decent bike network you can traverse an entire major city in 45 - 60 minutes. The problem is that most new cities are virtually nothing but asphalt and empty land in order to accommodate cars. I am sometimes called weird for saying this - but seriously - look at pictures taken at elevation and a modern "city" looks very sparse indeed.