Regardless of that, indeed, if either the MK pro or other pro player can adapt, that point is null and void.
Pros never use the "unorthodox", or, low tiers to play Meta either. Soon as you hit B tier and especially C tier, the matchups are more commonly going from a slight disadvantage to a decent sized one. In competitive Brawl, your aim in counterpicking is to choose the best matchup that you play well as, not the best matchup overall. Noone's going to counterpick Pikachu against Falco (Falco's worst match-up) if they don't know how to play Pikachu as an expert. This is why you see so many Snakes fighting Meta; their sub isn't Diddy or Falco (it's most likely Meta ¬_¬), and they play their Snake better than whatever other character they play that has a slight disadvantage or bigger, versus MK.