These will be very loaded statements, but the crux of this is that the overlap between PMs and PDs is so large that it's an unnecessary bottleneck to making qulaity decisions. To that end, I think PDs are better equipped to just own the full spectrum of work here because:
1. IMO, product acuity is on the decline across PMs—a sign of the times. Working with a PM that doesn't have a high caliber but has a lot of authority often leads to worse outcomes. I also think PDs can own aspects of the , which helps connect impact and product.
2. Esp. across smaller teams, I don't think it's that helpful to have someone own project management. Processes should be lean, and individuals should communicate and coordinate proactively. Having a PM that oversees process is an easy way to remove individual accountability.