This is my experience having been through 3 acquisitions.

In 1-2 years you go from: - operating well, get bought - throwing all the business infrastructure you've put in place that's deliberately different and better with what was before worse and slower - then leaders get replaced or leave because we can't do anything anymore - leaders start saying things like "we need to be more like a startup ", which would basically just hbe exactly what the company was pre- acquisition