Mosley admitted that weights slowed his handspeed. He said that he tries to keep his arms as flexible as he can. What you need to understand is its not like your legs making you a stronger faster runner, its more weight that goes with more muscle and that not only nulifies the gains from the extra power but hinders because of the added mass. When you get stronger on you lower body it effects the force that you put against the ground and allows you to explode with every step. when your punching your not push off anything with your upper body and therefore your merely have more mass to move, which slow you down.
Marquez has always had skinny legs, compared to Pac anyways. If JMM puts a lot of weight to his legs, rather than all of it going to his torso, then maybe his speed will remain intact.
Nacho would not let Marquez go into the ring if he is that bad. However, the fight has already been decided with Void's judges, ref, commentators, venue and everything else!
Throwing a punch is a whole body movement starting from your feet working its way to your fist where you tense at full extension, you'd have to have arnie arms and twig legs for there to be a problem, if he's built up the muscle in a functional way without doing silly bodybuildiing **** like bicep curls then he'll be fine, speed has to do with timing your whole body movement to be fluent and relaxed until the point of impact and then relaxing again as quickly as possible, if he's balanced the muscle he's put on he'll be quicker than before because to put on muscle you need to build up fast twitch muscle fibre.