That Pikachu in Jack's website is all technichal skill. To reach that kind of speed just takes practice, i wasn't suprised since most of that stuff i already do and know, but a trick that did suprise me was when he dash danced and forward smashed, omg what a friggin mind game, i been practicing it and it works like a charm ^_^. That was a very fast and technichal Pikachu, i love seeing Pikachu's play like that :D.
I still think that variety in the characters that you choose is very good for your overall game. I now play a Link, a very fast and technichal Link, and thats all thanks to my Falco and Pikachu, and now my Pikachu is a bit more on the mind game side thanks to my Link. Variety helps, and you should all know that. Sure, at the time to compete, it may be difficult to switch styles immediately, its pretty weird to go from a Falco to a Link, but you get to learn different traits, and you get a different kind of view, and that's going to help. I love switching to different characters, it keeps the game lively. But i always stick with a main character.
I do agree that switching main characters is a very bad idea though. Because your main character is the one you should focus on more than anyone else, if not, you will never improve to the level you want to be in. I practice other characters, but thats only to improve my Pika.