Many high performance 2 cycle engine are of the ringless AAC construction, Enya, Nelson and Jett come to mind. In the high performance class 2 cycle the benefit of the AAC is in dimensional stability at heat (power).

The proper measure is power to weight not displacement to weight. As for power to weight the 2 cycle has nothing to fear from the 4 cycle.
The 120AX is 3.1 hp @ 21 oz and the OS200 is 3 hp @ 31 oz with muffler 35 oz. Not that I'd rely on any data from OS to make my point or purchase.

You do make a good point that engine size restriction for classes where one wishes to limit engine power should be called out by mass not displacement. Duke Fox proposed this as a means to control the HP race we saw in many competition classes like pattern. But the AMA did not like the idea of a low RPM 15cc engine that only weighed 10 oz. Think of all the fields that engine could have saved being low rpm low power yet rather high torque if made correctly.