Title asks "Ask Slashdot: What Portion of Developers Are Bad At What They Do?"
Title actually means "Ask Slashdot: What Portion of Developers Are Bad At What I Do?"
If a functional understanding of a fairly specialized technological area is what you have in mind, don't assume it's widespread.
That's like getting bent out of shape if the local mechanic (fully trained and certified, even) doesn't know the detailed intricacies of ECM programming.
If you want a broadly expert Renaissance Engineer, I hope you're prepared to pay more than the usual one-trick-monkey pay. You're not talking about an engineer, there. Something more like Chief Engineer or Chief Scientist.