Arguably the PM role only exists because SWEs don't want to do PM work, and the industry acquiesced to this because SWEs are in very short supply - if you could hire a layperson (sorry) to take a few hours of non-technical work off a SWE's plate, it is worth it.

In a (hypothetical; not quite there yet) world where SWEs are in surplus, there is no reason to have PMs.

The really eye-popping efficiency gains from LLM coding won't come from doing the coding faster but from consolidating the PM, SWE, and QA/SDET roles under the same person. Then you'll start seeing startup/indie level productivity-per-person inside large organizations. Imagine Google is like 50,000 Pieter Levels.