Dick, you are absolutely correct about compression ratio.
There is only one way to calculate it on a 4-stroke.
On a 2-stroke, there are 2 ways. Full stroke or just that part of the stroke when the exhaust port is closed. The 2nd method alway results in a number in the range of 6-8.

Purpose-built aerobatic motors are designed for high power to weight ratio. Some hit the mark and others miss it.