A few points...

It's been my experience (after much experimentation) that less oil does result in *more* power at least when reducing it down to the levels I currently run (about 12%-14% depending on the engine).

The cause of this is probably two-fold. Firstly the fact that there's less incombustible oil entering the engine means a greater volume of air/fuel can be drawn in hence you get more power. Secondly, the pumping losses associated with drawing the oil in and pushing it out are reduced (which is also why lower-viscosity oil will produce more power than high viscosity oil - for a given ratio).

I tend to think that the Saitos are designed with a higher blow-by than many other 4-strokes which explains why they often (in my experience) have more oil exiting the breather. Yes, it's true that oil-in must equal oil-out but in the Saito, more of the oil exits via the breather than in many other engines where much of that oil would have exited via the exhaust.

The YS engine is a totally different kettle of fish it's pretty much like a 2-stroke where the intake charge passes through the crankcase - lubing the bottom end in the process. The YS doesn't rely (or want) blow-by to provide its bottom-end lubrication.

If you want to recycle your crankcase oil then the best place to re-inject it into the engine is (as someone else quite rightly pointed out) on the open side of the carby in the velocity stack or before the throttle barrel. That way you don't affect the dynamics of the intake manifold or introduce possibly harmful (to performance) pressure pulses into the intake system.