I think you are missing one big point, by staying inside a project you reach a tableu, a moment when you already know the tools, don't feel comfortable with some decisions or management but you keep working because you can bear with it. Moreover the tech stack gets more and more difficult to upgrade to latest trends. For me, the best switching project window is 2 years, you get to know the employee culture, network long enough to have good people foundation, then move on. The key is on the balance