Recently i watched a youtube video of mcgregor sparring with chris van heerden, and he got schooled. Mcgregor seemed to struggle with van heerdens footwork and ability to create angles, and against mayweather its going to be a 100 times worse.
Mayweather is older and he is not as fast as he used to be, but he is still fast. Although he does use his reflexes to complement his defence, they are not his whole defence. Mayweather once compared himself to roy jones saying something along the lines of, once his (roy jones) legs and reflexes go, roy is finished, but i will always have the fundamentals of my defence to cover up for the loss of my speed. I think he was right.
You were 100% right about it being an uphill task to find the key points for mcgregor winning , but i think you nailed it, if he is to win mcgregor has to utilise all the key factors you mentioned, take the boxing out of the fight and make it a war, but be smart about it, let go of flurries of punches and only put all his power behind the odd punch, the ones that have the best chance of landing.
Mayweather has not fought in two years but he has a world class stable of fighters signed to his mayweather promotions, i would very surprised if he does not spar with these guys regularly in order to pass on some of his knowledge to the younger up and coming fighters, which would have the added benefits of keeping him sharp and in shape.
Overall i think mayweather will win, but if mcgregor does he'll have earned his place among Cuchulain and Finn McCool. Great post i enjoyed reading it.