I gave you multiple examples where people used a brief window to stop an attacker. We both know it takes time for a reload. I can put two and two together.
If someone was shooting at you, would you rather they had one 30 round magazine or three 10 round magazines? I don't need a FBI study to know which one would give me a better chance of survival.
Do you honestly believe that someone will have the intestinal fortitude and reaction skills to try to subdue an active shooter within the first 10 rounds fired?
By the time he's ready for the first reload, people's ears MIGHT have stopped ringing and disorienting them. But, I highly doubt that in the time it takes expend 10 rounds, assuming he's as you've said over and over is just trying to fire the most rounds in the least amount of time possible, that anyone will be paying close enough attention to know he's reloading at that moment.
So, if you think the SECOND reload after 20 ROUNDS is the "window of opportunity" to flee or fight, that is no different in terms of your arguments than the shooter using a 20 round mag and not having to reload.
Your logic is so sloppy -- you ignore the obvious human factors associated with being shot at and pretend this is an academic experiment with controllable variables.
I guarantee anyone can fire 1 rd/second, which means the first 10 seconds of the massacre is all anyone has to think, decide and act when the first mag is empty. How many do you think are even in a position to view the shooter if they are hiding? How many while running away will do an about face to fight?
If all the stars and planets align, and someone with proximity and opportunity AND COURAGE goes for the shooter, the mag change will not be the deciding factor. The instinct to survive will be enough.