Planning a lesson that is being observed for performance managment takes at least 2 or three hours
Do you really think you need to spend 2-3 hours planning each lesson? I had some great teachers at school and I sincerely doubt they spent anywhere near as much time as that planning a lesson.
If you have teachers of the right quality, who are sufficiently motivated and know their subject, you wouldn't really need to do a huge amount of planning. Unfortunately most of the people I know who would have made great teachers are either demotivated and stressed, or have left teaching.