All valuation is based on speculation. “The numbers” are always subject to change.

I guess I was thinking about how a more regular/predictable business would usually be sold by its owners for a multiple of its yearly revenue, for example.

Would the same apply to unicorns? Probably not, because they're special.

Both situations are still betting on future potential, either via earnings maintenance/growth, or via betting on being able to sell the equity at a higher price to a subsequent buyer.

Matt Levine has a great newsletter where he regularly delves into questions like this. He recently wondered, somewhat seriously, if the era of valuing stocks based on fundamentals was a fad that's now over.