There is a world of difference in a water cooled engine like a boat engine and an air cooled airplane engine. The heat-cool cycle has been recommended by everyone who has worked in the model engine industry for years.

With a ringed engine, you need to run it rich some to seat the ring.

An ABC engine is really hard to hurt is you just crank it up, lean it out, then back it off a little and go fly. It is my opinion this is the reason nearly all engines are now ABC type construction. The great numbers of new people with no knowledge of engines and no desire to break one in has made ring engines less desirable from the manufacturer's standpoint.