"In the airplane, build an intake tuned to 6000rpm (give or take), build
a stainless steel muffler and your ready to go."

You made the point quite well that I was trying to make humorously. The true test of an engine is not whether it powers a car or not. The real issue, does it work well for a given application. If yes, then it is a good engine for that particular application. The rotary does have its applications, not just cars. And yes, it does work well where a constant rpm is desirable.

Using the analogy of "does it work well in a car" is parmount to rating UL engines by "does it work well in a snow mobile". Pretty darn absurd I would say.