Why? that was before we saw speed feats from 7G Gai. Does that mean he'll always be the fastest Man without being surpassed? Tobirama was once named the fastest man as well.
Gai made contact unlike Minato did. Even twice or so. He didn't do anything? He forced a Juubi Jin to block and evade his attacks, didn't get struck or blitzed in a CqC and left him surprised twice. That doesn't show anything? It won't have shown anything if Minato did something won't it or if KCM Naruto didn't evade Ay at top speed? He fell to the ground because he was weakened before the fight as shown with Lee and Ten Ten.
Take a look and you'll see it was V2
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. He blocked Ay and that was all to it. He was sent flying cuz of the power punch but he reacted.