Given the amounts being raised and spent, one imagines that the ROI will be appalling unless the pesky humans learn to live on cents a day, or the world economy grows by double digits every year for a few decades.

If the entire world economy starts to depend on those companies, they would pay off with "startup level" ROI. And by "startup level" I mean the amounts bullish people say startups funds can pay (10 to 100), not a bootstrapped unicorn.