One of the industries is
Computer Software: Prepackaged Software 112.17% 17.81
And that doesn't take into account that Substack is doubling every 6 months
So Substack is 2 doublings or 12 months away of growth from bringing it's multiple to the industry standard, that might be an aggressive evaluation but it doesn't seem insane.
[0] https://www.statista.com/statistics/1243565/substack-paid-su...
* Not to mention most VC deals are sweeter than a pure purchase (in terms of being protected from a down round etc.. *