The desirability of the SPE engines is not so much the power but the power to weight ratio. I don't think anyone ever said the SPE engines were more powerful than the Zenoah's. There is better than a 1 lb weight difference between the G26 and the SPE or BCMA 40CC engines. If you have a plane that needs a lot of nose weight, then the G26 would likely be the way to go. The SPE 40 opened up 3D possibilities for lite airframes. On some aircraft, the airframe just would not handle an engine the size of the Zenoah, but it would handle the SPE 26 size. I wouldn't read any more into it than that.