... and when you give people direct access to the front buffer, they write code that tears or generally scans out incomplete renders and users end up blaming the operating system.

Compositing is a good thing, and in the vast majority of cases its latency isn't actually intrinsically higher than writing directly to the front buffer. Certainly its intrinsic latency is never higher than writing directly to the front buffer if you build a system without visual artifacts. (Because at the end of the day, all compositing does is shift around who does the job of putting things on the front buffer; the jobs themselves stay the same for all practical purposes.)