The world absolutely doesn't begin and end with middle class in the USA. But you're just wrong to say "DoorDash mostly solved problems for a small part of reasonably wealthy people, mostly without families, living in big cities". There were times it or a competitor were a godsend for my not-quite-middle-class sister, with five children to feed, who lives in a small city a half hour from Cincinnati.

It’s not exclusively for middle class, sure, but that’s their main target market. It has other users, and it’s great if it’s solving their problems as well.

I’m not diminishing their impact (although I question lots of their business practices). But it’s not the most important tech, by a huge huge margin.