Variations have changed match ups drastically in other games. Just look at the Arcana Heart example @haketh gave (which I will quote once again).
Tyr Arcana is something of a hard counter for Cathy so most players using her will switch Arcana to something like Tempestas/Wind when their opponent tries to use Tyr to counter her.
Are we really going to base MKX tournament rules off Melty Blood? Most likely those rules are carried over from the Japanese arcade scene. If we went by Japanese rules, we'd probably also have all tournaments be character lock throughout the entire tournament and every match would be a first to 1, and single elimination.
They carried over to the American scene & they ran with being able to change because it made sense. They did phase lock for a little while & it just wasn't enjoyable like letting Phase change happen, that's why Frenchbread left it in the game in the first place. And note the only touranments that are character lock usually in JP Tournaments are Team Tournaments or specific Qualifier style tournaments like SBO/Arc Revo/Gods Garden. Melty tournaments are not character lock & it's a 50/50 for whether their double elim or single. Only smaller Melty tournaments were Single Elim.
