Yes, it's true.
While the advantage of a single DICKtator is that it's next to impossible to subvert him/her, but if he/she gets subverted, it's over.

As for people making their own OSs, I guess that will become possible only after RISC-V becomes common use.
Back in the 90s it was still possible, which is why so many different OS's existed back then.
But then IntHell and AMD on the CPU front and IntHell, ATI (now AMD), and Nvidia on the GPU front NDA'd the crap out of their architecture, and the only survivers were Windblows, macOS, Linux, and BSD, because making your own OS was simply made impossible (perhaps except for things like TempleOS, React, Haiku, and MikeOS, but those who made it are/were VERY dedicated).