Why is Counter/Close Combat Machamp rated B for attack?

Dynamic Punch is rated higher because it's a two bar charge move, so it's faster to power up. I personally prefer Close Combat because it does more damage and I think faster charge moves that do less damage are better suited for defending than for attacking, where I prefer charge moves that have more of a knockout punch, like Solar Beam, Hydro Pump, Hyper Beam, Overheat, etc.

I'm guessing you mean in one specific video, there was a 1 second difference, in one particular battle, against a specific defender. The exact battle time depends on numerous other factors such as the defender and related defender moveset, dodge strategy, and attacker skill. This can result in the battle ending at different CC charge levels, leader to larger time differences.

A sim across all Blissey movesets and multiple dodge strategies found C/CC took an average of 5 seconds longer than C/DP and also had worse health... quite a significant difference.

i've seen the video. Maybe it's because HP left after the battle, 82 > 60

I actually prefer CC as the longer cool down for DP leaves you open to be hit by charge moves.