I believe you are getting all worked up over nothing. Extreme spread in a revolver can be several things. One of the most common is the chambers may be slightly different sizes, it happens. That is why if I were to worry about it I would mike everything and even record lot numbers of ammo, as that is also a know variable. You will generally find more variation from barrel to barrel than by a short barrel. Pythons have always been slower than Smiths, for the same reason they are more accurate - A tighter barrel.
The only time the 9mm comes close to the 357 magnum is where light 110 grain bullets are used in the 357 Mag.
I could keep all six shots in the X ring of a B-27 @ 25 feet (not yards..Im decent but not that good) shooting rapid D/A - but - the ejector would tear the living crap out of my hand as the gun recoiled.
You are doing something wrong. You should be nowhere near the ejector (which is shrouded on a 66) during firing.