You failed to simulate a hard effort while riding. Coasting is a relaxed form and and easy position as to "wave" if one chooses to. I wave most times out on the bike. But in a concentrated effort, while hammering on the bike, both hands clutched on the bars, I will by no means lift my hand to return a wave. As doing so my jeopardize my health with a nasty crash. I ask that you please add another test, this time going in an all out effort, eyes fixed on the road ahead, concentrating on your position, form and speed, cadence and projected power output. Then, think of waving added in. If this is possible, then you are not training hard enough. Casual riding, yes, by all means wave at the fellow rider. Otherwise, get your mo-jo on and RIDE!
This true, and a valid criticism in my humble opinion. I had originally intended to use my heart rate monitor to correlate against waving, in order to determine to which extent my effort is damaged by waving. But there were so many variables affecting my heart rate that I gave up that line of investigation.
I'd love to test it the way you suggest but with no power meter I'm afraid that the data would be subjective and otherwise non-repeatable. I did consider trying a pair of time trials on the local MUP, once waving to everyone and once not - my difficulty there is that not all MUP users share our high regard for science.