Loosely speaking..........

Horsepower is torque X rpm

Since 2strokes operate at higher rpm, they could produce the same torque as a slower engine and they'd have a higher horsepower rating, right? loosely speaking.....

The real measure to compare would be thrust. Nobody publishes that for good reason. But there is a thrust program somewhere around here on the internet. If you were to plug in the prop size and rpm for the appropriate size 2stroke and get the thrust from that prop, and then compare that to the trust from the appropriate size 4stroke and it's prop, you'd have a better comparison. And it would show thrusts that were more equal than were the horsepower ratings of the two engines.