Well I said theoretically if you had noticed that a two stroke engine is more efficient than 4 stroke engine.
You only taking into consideration of the unburned fuel but leaving behind every other factors.
Most efficiency lost in a mechanical engine are through the exhause heat not unburned fuel (around 65% loss of total energy). 4 stroke engine does waste more energy theough that. at least 1%.
2nd most killer are the friction which abrubptly decrease the efficiency. In a four stroke engine you have double the friction not only in the piston but also in cranks and flywheels. You may notice that a two strok can run just fine with lubricant mixed with the fuel itself. But in a 4 stroke engine must have separate arrangement for lubricant.
3rd most killer is the exhaustion which requires a full stroke for a 4 stroke engine wherea a two stroke engine just finish that in ints power stroke.
If you take into consideration these factors and do your calculation than a 2 stroke engine always gives you more power from the same amount of fuel.
But most of the two strokes are used for low cost engines where other factors like noise, air pollution etc are not major factor. As 2 stroke engines are designed for low cost so does scrap most of the goodies, like sepearate cooling and lubrication system. Users just have to mix lubricant with the fuel which is a killer and is the main reason for unburned fuel and dark smoke.
I hope this will clear the confusion.