Pikachu's problems lie in it's lack of range that force it to commit to many attacks, but Uair is one of the moves that has both super low lag (such that you can SH waveland it) and actual disjoint, so it's pretty damn safe if used correctly. The speed, above average disjoint, and low knockback (because low damage) all usually guarantee another hit on the opponent, so another Uair, Nair, or Bair can cover the opponent's DI when juggling them. Plus, Pika's U smash and gimp game means he doesn't have to rack up as much damage to get kills. Uair is already one of Pika's most versatile and unique moves - the 4 to 7 damage buff is already fantastic