Turns out that under certain conditions, such as severe exhaustion, that "sus filter" just... doesn't turn on quickly enough. The aim of passkeys is to ensure that it _cannot_ happen, no matter how exhausted/stressed/etc someone is. I'm not familiar enough with passkeys to pass judgement on them, but I do think there's a real problem they're trying to solve.
Something "$5 wrench"
Besides, if you ignore security alarm-bells going off when exhausted, I'm not sure what solution can 100% protect you.