Word. IMO, one of the most important, yet underrated duties, of a good manager.
As a leader, you want people to crawl over broken glass to want to be by your side. If not, you end up like North Korea, where you have to sell why people should stay, sometimes eve being dishonest and intimidating in the process. Seeing the latter happen is always a sad sight.
So do not under-estimate the impact of retention.
I think GP was more saying that improving retention, at a % level, is a slow ship to steer. (At least what is available at the manager level.) Decreasing retention across the org in the long term doesn’t happen overnight, and it can take a while to observe whether the effect is trending downwards or upwards. (And also depends on what signal you use - people actually leaving, or people talking about leaving!)