[JFreak]

Before clean install it is useful to throw all plugins to unused folder and try again. Even a single bad behaving plugin may cause that. But if it happens with stock plugins only, then yes, clean install is the way to go. But if getting rid of plugins helps, then the task is to find the offending plugin and either update it or stop using it.

I myself only really use clean installed systems, but after a major OS upgrade I naturally test "upgrade the apple way" and every single time my benchmarking shows it is a problem. Even if I do not have random problems that are hard to pin down, overall performance of the system is sluggish.