[whatsac0mput0r]

You're missing the edge, which is very very broad.

Suppose your employer wants your web app to interface with an industrial PLC, or fetch data from a car's CAN bus, or talk to a vending machine (ironically the sort of machine that Java was originally designed for).

Most bootcamps don't teach enough fundamentals for someone to figure out how to write both client- and server-side code for those sorts of situations.

Or on the other end of the spectrum, could you write hypervisor code to manage the sort of mass-scale VM deployments behind most cloud providers? It would be very difficult to be an expert on the "full stack", if you think about it.

So...tl;dr, most of the application layer? Probably the physical layer too, any how many of us really work with the link layer?