[dijit]

10,000 hours, whether true or not, is a ballpark and even if it's patently untrue: it will always require some non-trivial amount of time to get good or master a particular subject.

Not all subjects are equal, granted.

having overlap in knowledge between roles is also somewhat granted; being a complete master in backend gives a person a lot of knowledge towards being a sysadmin (maybe even 60-70% of the way to being a master in that direction!);

But, you've failed to convince me that any single human on earth can do "everything"; even if a person could literally master all technologies in use (not counting your strawman of driver programming) then there would still be a discipline mismatch.