Yes this may go outside the original topic. But when pondering 2-stroke engines, you should not concentrate on single details. You are so correct saying how simple it looks but in reality there is very complex interaction between all those simple details going on when engine is running. The magic word is harmony.
I am quite sure that the amount of air going in is not far from calculated value. Of course there are some losses but not so big as elsewhere in the system.
I really can't see that the amount of fluid inducted each stroke will ever equal the swept displacement of the engine.
Sure if you had a Wide Open Throttle with a ram air intake as found on a speed model (suggested above) you might approach it as a theoretical maximum but in stunt use we are far from that with maximum performance way down the list in favour of a more 'draggy' fuel draw.
Are you suggesting that no matter what size venturi (or indeed any gas induction passage) you use that they all will allow an almost 100% fluid draw?