Changing managers and team leads most likely means changing how you work or what to prioritize as well. I don’t believe that only the heads are replaced and everything stays the same. Every new manager usually has new brilliant ideas on how to improve stuff. Even if your lower level job is safe, the entire restructuring of projects and teams might be more than just something to brush off and continue working. Employee A gets promoted, B gets fired, C gets into another position - warranted or not, I don’t think they’re now more productive than before, I even doubt that they’re even as productive. This entire process costs not only resources, but also work time, until everything is settled.