You describe problems that were solved long time ago and not even in IT. Spec-first approach works fine in the long run, it just requires a bit more process mat

You describe problems that were solved long time ago and not even in IT. Spec-first approach works fine in the long run, it just requires a bit more process maturity than you can find in a typical startup. For example, the problem of matching commits with specs doesn’t even exist in environments without continuous deployment (which is rarely a real necessity and often is even undesirable). You just tag your releases in VCS (can be easily automated) and track their scope in documentation (job of responsible product and engineering managers which know what goes live and when).