Linux to me is an example of the wrong thing at the right time. Linux embracing Posix and fully supporting Intel gave programmers exactly what they wanted right at the nascency of the dotcom boom. Apache, MySQL and PHP needed a home that wasn't Windows ... and Linux provided that home on the best dollar-for-dollar processors on the planet.
If Motorola or IBM had challenged Intel with cheap, better processors then history might have looked different because Linux wouldn't have been a solution on those platforms.
Linux works well enough I suppose, but the fact that we have this gigantic mess, where we run an OS, and then run a hypervisor on it, and then run more copies of an OS, and then finally get to run our application code, tells me something is quite wrong.
The fact that unikernels are even a thing tells me that people DO feel the pain of monokernels and yearn for something simpler. Securing a monokernel like Linux, even one so open and scrutinized, is really, really hard. There is just so much surface area in the kernel to attack. Everything is so heavyweight.
I think Tannenbaum was right, but he just wasn't enough of a hacker to get things done in time to catch the wave that the dotcom boom created.
To me the dream would be something like Google's new Fuschia OS where everything is capability-based so security is built into the OS concept from the very beginning.