I really like the idea of using the existing Amiibo in sports games. Perhaps a little like Blood Bowl, a Mario Amiigo gives you a Mario themes team, and will play VERY differently to a Kirby or Sammus based team. Sure, pick Soccer and then watch as your Mario team runs around throwing fireballs and coin punching while the Kirby team sucks in your guys and steals their powers, while hitting you in the face with a hammer.
So 1 Amiibo gives you an entire team, themes to that character. Soccer, Baseball, etc. Only 1 Amiibo requires, but if you wanted to experience a very different team, then buy a different Amiibo. Oh, and make the damn game online :-)