Madara getting pinned down isn’t due to just Gai’s speed, it was due to the nature of his evening Elephant punches that created a combo.
Madara gets hit by 2nd punch because he’s still holding the air pressure from the first, this is just a speed vs reaction feat, the affect of the first punch comes into play here.
As I said, Madara successfully react to ALL of Gai’s initial attacks, which is a straight speed vs reaction scenario, with one even faster than the evening elephant punch.