To be clear about this, I have potentially unique insight here because of my own work on OS design in late 90s/early 2000s. I know what's possible, what I (by myself, in assembly, using MS-DOS, MASM 6.11d, and only a floppy drive for testing) was able to achieve. I know there are also people "called" to OS design (very few though). It takes something atypical to do it.
You garvley underestimate the work required to make a operating system, let alone a kernel. The major problem is not the fundamentals, it is the drivers. Without drivers, you can't use your computer. Period. And this is where our current, lowest, battle is, seeing that the hardware we use doesn't get crippled, and so that we get access to documentation so we can write free drivers.