Let me know how I can unbundle Safari from macOS or iOS.

Go ahead, I'll wait.

It's possible on the Mac, but it's not easy. Apple uses an immutable system volume on macOS, so you can't just delete the Safari app like you would a user-installed app. To actually delete Safari you need to disable System Integrity Protection and reboot.

There are plenty of Linux distributions that use immutable root volumes. They protect the user in a huge number of ways by preventing the system from getting hosed (either by accident or by malicious unauthorized users / malware). Apple made the decision to do this for their users, and it has prevented a HUGE amount of tech support calls, as well as led to millions of happy users with trouble-free computers.

It also hasn't stopped users from installing Chrome and/or Firefox on their Macs, and millions of ordinary users have.