Counterpoint: my burner gmail for account creation with 30k unread emails, mostly spam. Also so much spam gets into my university email accounts, much of it from predatory journals offering to publish anything and everything.

For the university accounts, I'd say only 80% gets trapped into the spam folder (my gmail is an absolute mess, however), but so does 5% of actual relevant emails and conversations, so I'm forced to inspect my spam folder pretty regularly which kinda defeats the purpose of hiding it from view.