I proudly print my entire KDBX file including passkey private keys and I encourage my elderly parents to do so too.
Lightning strikes (and assisting people with cleanup and repair from them) have taught me that there are definitely a class of threats that will leave me with paper but possibly no technology until I can go buy a cheap laptop to restart my digital life, SO BEING ABLE TO BACK EVERYTHING UP IS ABSOLUTELY ESSENTIAL.
His website says he's in Boston, so I seriously doubt he's ever seen what lightning can do or dealt with a hurricane or tornado.
In general, if you're in the FIDO Alliance and had anything to do with the kind of micromanagement that passkeys can allow, FUCK YOU. Go get a job at Walmart as a greeter. We'll all be better off.