>Complicated to implement, yes. Complicated to read and understand why the browser is doing x? No.
CSS, for one, is notorious for being complicated to understand, with tons of complex cases, especially in the layout department, where whole cottage industries of "tips" and "workarounds" for the simplest of stuff -- and I'm not talking browser incompatibilities -- thrived for decades (until, at least, flexbox and the like).
I'm not sure if end users are the people W3C is trying to satisfy. Browser vendors do enough of that. If anything, they're trying to satisfy media corporations that want DRM standards, or ad corporations that want pervasive tracking.