Regarding the mantra..."There is no overtraining" Just because you can handle large amounts of volume doesn't mean it's needed. That's the crux of the issue. Just because the body can tolerate something doesn't mean it's a necessity for progress. This is simply poor logic.
Last time I checked, lifting theory has a PR of zero.
On the Internet, everyone squats. In real life, the squat rack is always empty. You figure out what this means.