Well, "adapt" is the key word here.
A Level 50 Amiibo isn't automatically really good at the game. I think the level just reflects their learning efficiency. However, a Level 50 Amiibo still won't do something you haven't taught it. For example, people attending those recent Amiibo events trained an Amiibo to Level 50 without ever using any items. Then, when it got to Level 50, they put it in matches with Items on. And the Amiibo didn't understand what to do with them, and simply ignored them, or stupidly stood beside them. It was only after the Amiibo was specifically taught to use items that it would start using them.
Overall, we'll be able to test it when it comes out. If I can make a Level 50 Rosalina efficiently control Luma, travel under the stage, or other such shenanigans, then I will consider them a well done addition, without question.
EDIT: GameXplain has a slideshow video of them:
Yeah, I definitely think Yoshi looks the best. Though Samus, Pikachu, Kirby, Fox, DK, and Mario are pretty close behind. Link honestly isn't too bad either if you don't consider the pole and the sword. And Peach's face is off model, but she's fine otherwise.
Marth is just too much though.