I really can't comment on which type of engine lasts the longest since mine usually last until I'm tired of them and something newer and "better" comes out.

It is my opinion the reason nearly all 2-strokes are ringless, ABC type construction is the flood of new fliers and the reluctance of most to break in their engines. In this nearly instantaneous world, we don't went to run tank after tank of fuel through an engine to get it to run correctly, we want to go right now.

With a ringed engine, you risk warping the ring if you don't run it somewhat rich at the start. Slobbering rich for a couple of tanks is better and a gallon rich is best. I did this to all my Saito 4-strokes and they run great.

An ABC engine, for all practical purposes, is very hard to hurt if you drop it in a plane, lean it out and go fly. Running it rich is bad for engines of this type. So the manufacturers are probably thinking that it's worth the slightly higher manufacturing costs of the ABC type to let people crank up and go. They probably don't get as many returns or complaints, either.

Joe Doaks can put his new Widget .46 in his new fun fly plane, crank up and by the time he has a couple of trim flights on the plane, the engine is mostly broken in and reaching max power.

His buddy with the ringed engine, a 4-stroke, for example, is still putzing around, running rich while Joe is scooting around the sky.