It is ironic that a codebase with so many classes is likely to occur precisely because of dogmatic adherence to those "best practices" which were originally intended to improve code quality --- aggressive refactoring/modularisation being a likely culprit. What I think they really need is not more design, not more architecture, not more of anything but KISS and YAGNI.
The thing that having an overall architecture buys you is conceptual clarity. That lets someone much more easily understand what is going on. You need to have a minimal set of ideas that are well thought out and explained.
Just saying "YAGNI" and "KISS" doesn't actually make the resulting code simpler. Why? You do have some things to build and refusing to lay out a plan for what that is going to be doesn't stop that. It just means that the complexity doesn't have a clear narrative
It seems to me your point about KISS and the author's observations are compatible.
Facebook is successful for reasons that have almost nothing to do with their code, however, and as long as that's true there isn't a reason for them to change how they develop their software. In that sense, code quality doesn't actually matter (at least, until it does).
