I'm assuming you are referring to natural speed of both hand and feet? If so, i would agree. Mayweather has lost a lot of his bounce in his legs and that's obvious in his last 2 fights. If he still had the ability to bounce in and out quickly, he would utilize this but he seldom does anymore. But his skill level is so high, he doesn't seem much affected but has adapted to fighting more flat footed. His reflexes are still amazing.
Pacquiao fights the best fighters today. He is not declining..not much at least- Pacman has no problems with JMM. Look at scorecards lol.