As long as apps are kept up to date, I'm not sure that OS-level security updates make much of a difference. Most breaches happen due to malicious apps. I haven't heard of any cases where somebody cracked the OS security and accessed user data.

Most of the world is not using the latest version of Android, and you don't really hear about viruses/malware like we used to with Windows machines in the '90s and '00s.

There's also lots of modern budget phones that are using 5 year old processors, shitty cameras but modern OS support.