I don't see the need to replace the mascot just because it's not "good in battle". Even more so, mascots aren't suppose to be the best at what the "sport" is. For example, I doubt football (or soccer, for those who call it that) mascots are tailored to be the perfect football ace, nor are the people who wear the disguises required to know how to even play it. They are good at their job, and that's how they should be. Pikachu does his job pretty well; he looks cute and appeals both genders. Also, while Raichu isn't topnotch, both he and Pikachu are pretty decent battlers on their own right. Sure, they can't easily beat a Mewtwo, but does that really make them bad? Besides, one does not simply replace the mascot, a Pokémon everyone knows. With that said, I think Pikachu is a wonderful mascot and Pokémon in his own right. He is a fine ambassador to the series.