Personally I want always to have a pre-upgrade backup before upgrading, and personally I will always download that backup before proceeding, because I don’t know the worst of what might happen if the upgrade breaks. It’s also a useful reminder that I need an offsite backup as well as online backups, when an upgrade comes around.
I suggest it would be an improvement if the upgrade page could check for a recent successful backup, and perhaps even better if it could note that a downloaded backup adds more safety.
For me, “recent” means within 60 minutes.
If the backup file has an access time the same as the modification time, that very likely means it has not been downloaded.