CEO is a hard role not because of domain area but because of risk and uncertainty, both of which tend to be low when you're "at the bottom of the food chain."
In my engineering school, mechanical engineers were taught the basics of electrical engineering.
There is a lot of value in gaining a good amount of breadth before specialising, even if just to ease communication with specialists of adjacent fields.
Lionel Messi doesn't try to be the best header or best defensive midfielder. He focuses on dribbling and scoring goals.
In the latter, he also touched some GTK code: https://github.com/torvalds/subsurface-for-dirk/commit/c0adf...
Trovalds has much more breadth than you give him credit for.
I do think he's in the top 5% of MDs, so of course we can't expect this of everyone. And specialists obviously specialize. But there is a large segment of the profession that requires a wide breadth of knowledge in a domain that frequently changes.
BTW, my career has been focused on development, but I still try to maintain enough knowledge that I could jump in at any point of the stack and be useful.
Maybe this site should add a CEO skill map!
Edit: For example I make a living doing web development and rarely using a framework or a package manager in my projects. Knowing their value sure helps in a CTO like role, but you can deliver real value and state of the art websites and apps without them.
A lot of stuff, true, but nothing particularly challenging.
I would say the hardest part is CSS, but using a framework like Bootstrap and then googling the little problems "how best to X in CSS" usually works.
CSS is hard. Even for people who have been doing it for decades. I am one of those people who can do whatever can be done on Bootstrap, but from time to time, I still struggle with CSS. It is getting better these days because browsers are co-operating and don't have their own flavour of CSS just to break other browsers.
My SPA does use HTTP/WebSocket, it's served with nginx, uses a postgres database, but this is backend stuff.
Just for example, Devops engineer lists Mesos, emacs, sockets, and virtualization. Other than know that these concepts exist and a 5 sentence description of what they do, you don’t need to intimately understand them. I haven’t gone through the other roles but I’m sure they’re the same.