>"It's really tempting to believe that with the right hardware, we can put everything on one powerful and inexpensive box"

This is what I have. 2 boxes only. One on my own premises in Canada and another on Hetzner in Europe. Each one can go down, no sweat. Also I do not strive for "live uninterrupted updates". All my applications and processes allow for short disruptions not to interfere with the main course.

Also I write native servers in C++ for backend and they process thousands of requests per sec without breaking much sweat. Way more than my business would ever need.

Same situations with my clients as well with the difference that for legal reason they rent computers or whatever goes as such from Amazon or Azure.