Floyd Mayweather, Jr could have finished JMM if he kept up the aggression imo.

Pretty much!
If Mayweather would have pressed harder to finish, that would have opened a door for Marquez that Mayweather did not want to see.

Mayweather was to quick and fast for Marquez to stand a chance at center ring in a pure chess match.

The Mayweather fans looks at it as Mayweather having better boxing skills than Marquez, but that couldn't be further from the truth.

You take two equally skiled fighters and have just one of them be quicker and faster with the other not having a single physical advantage, then you're going to get what you saw in Mayweather vs Marquez.
The only chance Marquez had was for Mayweather to uncharacteristically turn to stalking. That's the one chance Marquez had because Marquez is a better counterpuncher and overall better combination puncher than Mayweather is.

Mayweather knew that going in so he wasn't going to go that route and risk the chance the fight turn competive.
Sorry, but Mayweather doesn't look out to please the audience like that.

 

Do you think Marquez would beat Floyd if they were the same size?