I disagree with the last point. Understanding the low level details of a system definitely makes a developer more productive.

When I am working on an iOS app and I get stuck on a bug, I can open a disassembler and immediately figure out the cause of the bug. The same goes for a ruby developer who wonders why their queries are taking forever or a front end developer who doesn't know why their interface is dropping frames.

Any serious engineer should be able to fix these problems on the spot if tasked with it.