Ryobi vs Zenoah

Back in November 2004, Walt asked the question of the cost of conversion of
a Ryobi 31 cc. For my part, I have done this conversion and I have a great
engine for less than $150.00 (less than half than comparable "model
airplane" gas engines). With that said, I just read a review of the Zenoah
G26 in the latest issue of Fly RC mag. Guess what? My weed cutter Ryobi
conversion turns a 16x10 prop at a higher RPM (8,100 vs. 7,260) and idles
lower (1,400 vs. 1,860) than the G26. And my tests are at 5,500 ft altitude
with 15% thinner altitude, which knocks the crap out of engine horsepower.
As for weight my Ryobi is almost 1/2 pound lighter (51.1 vs. 58.3 oz.). I
should add that I added a homebuilt electronic ignition and dumped the stock
one pound flywheel/coil assembly.
Granted my $150 total cost doesn't include some of my labor and my friends
machining (I owe him a lunch) and my 31cc is 22% larger displacement that
the G26 @ 25.4cc.
Therefore my observation is that the engine conversions are at least
comparable to other gas engines in their displacement class and cost less.
What's wrong with this logic?