Realistically email hosting is probably a safe-ish business. The required software is already more or less commodified(and the sort of people who pay extra for Proton rather than just using gmail or whatever their ISP points them to are the ones who specifically Do Not want you churning the UI all the time), just not desperately entertaining to administer; and the major challenge(even if you just ignore the amount of admin required to stay on top of security risks when internet facing and hope to get lucky) is achieving the necessary scale and stubbornness to get decent odds of delivery on the various major recipients of email who, at least initially, shoot the spammer and ask questions later or never if novel senders start popping up.
You could already DIY-mailsever in a fairly short span of time well before it became viable to ask a bot to do it; people just prefer not to because babysitting postfix just so that you can get rejected by the various services people you are tryign to reach use is not terribly rewarding.
It's not necessarily a glamorous or high margin sort of business; adequately competent hosted email isn't a wildly differentiated product; but people tend to not enjoy changing email addresses/repointing DNS/migrating mailboxes; so it's not a super cutthroat commodified market where people switch every quarter for the absolute lowest price. If you don't do anything particularly obnoxious or try to push price hikes there's a decent amount of inertia.
However, and this is what makes this guy's ranting seem so unhinged, it's precisely not the sort of business where you'd expect some sort of "AI transformation"; or a bunch of panting about whether the stack has velocity. Proton's config is a bit more fiddly than average, because it is supposed to provide better than 'just trust me bro' privacy assurances; but they do operate the fax machine of the internet age. We call it "email". And their customers are paying them for mailserver stay up; not the agentic everything app.
I'm not sure if this guy is butthurt because he didn't manage to score a nobel during his science time; or because he's not looking at an altman IPO; but the fact that he is screaming like a lunatic about “ruthlessly smash everything that stands in the way of AI velocity" when he runs something that is, as a feature, supposed to be a deeply boring utility suggests profound temperamental unsuitability.