You don't have to stick to their software either, use DrawIO if that's what you prefer, but understand the main concepts that C4 is trying to impart about the separation, what goes on the arrows, and how useless icons can be.
Precisely. Any time someone utters the descriptor "best practice", at best, you do yourself a favor by examining it with a critical eye and judge whether it is a good practice to follow (and a good fit for your project) or not. At worst, you beat back the consultants framing it as "the one and only way to do things (with the implication that everything else is wrong)."
But yes, this is fundamentally an OOP thing, and especially the component layer is very much just fantasy. In no real OOP software do these meat reusable components not have super strong binding to each other. Yeah you may have the SignIn controller and the ResetPassword controller both talking to the SecurityComponent, but in the end that's guaranteed to be implemented in such a way that you cant use any of them without all the others connected, and its likely that testing this means writing a mock for each of them that is so complex it may as well have its own tests.
They are thinking of their problem, and building their solution entirely out of blocks made from the words that make up the problem. "We need users to be able to sign in and reset their password" becomes SignIn component and ResetPassword component, when really this is just a matter of changing a hash and possibly some encryption keys, and could just be a handful of validate(), reset() et al functions on the security module.
Your comment is useless to me; so ultimately I'm not likely to give it any credence.
Whats your background that you have simpler alternatives?