Use 30 weight oil if synthetic, and 40 - 50 weight in mineral oils. Synthetics have a much higher wedge film strength, and that is why they are called "light running" oils.
Do not listen to, or try to compare the two stroke with the 4-stroke, nor use outboards with needle bearings as example. This thread is about a plain bushed conrod bearings in a small two stroke engine. The smaller the engine, the larger it's craving for oil, because less fuel passes through. With less fuel, also less oil is provided.