The slinger does exactly what it says–slings the oil off the shaft. But there is much more to the story. After is is slung off, where does it go? Well, the "where" is it is sucked back down to the intake manifold for re-cycling. There are passages in the crankcase casting for that oil return.
No, the system is not perfect, but it is very amazing that it works at all. In fact, it works very well, and was used on tons of motors, even as large as the 12hp Gales.