This is an interesting take, because for me, the former, for proprietary-format/online-only/app-only books, which I thus can't back up, is obviously vastly more likely to become a real issue than the latter or with digital PDFs or similar. But we all assess risk differently.
And sometimes positive things happen too - if WotC are doing well when 6E rolls around, and want to transition people away from 5E, I'd be unsurprised if they sunsetted 5E support on Beyond, but provided all the books we'd bought to us as PDFs!
Personally, I'm a bit vexed because if I blew what, like £140 on the three new rulebooks in digital and then say, Sigil goes live and rapidly starts showing enshittification (which I think is actually more quantifiable than you're allowing, it's not all airy-fairy stuff - specific examples have been provided - it's fine for those to not matter to you, but that's different from them being not quantifiable), because that'd be a huge proportion of TT RPG entertainment budget (and very noticeable portion of my entertainment budget) gone for that year. Like I actually would regret it kind of money. Hopefully friends will buy them and the relatively generous design of the DDB will let me piggyback off them until Sigil releases and we get a better picture of how much Sigil and DDB will actually interact, and just how shark-like the monetization on Sigil is.
I had a friend lose all of his books because his car was broken into. We hear all the time about people losing everything to floods and fires. If I was paranoid I could spend a few hours and download the books to PDF.
I mean, if the worst happens of course I'd be miffed. But there are no guarantees in life and stuff happens.