If the problem is that Pichu dodges attacks by standing in place, the solution cannot be "in practice, Pichu will jump into your attacks." If you're throwing out attacks that only hit because Pichu is jumping around, players are going to learn to stop doing that. Pichu has a powerful tool, and sooner or later, players will figure out how to abuse it.
Bair is arguably Wario's best approach option. Fast, powerful, and safe. But the main reason it's safe is because it gets Wario out of the way before shieldstun ends. Since Pichu doesn't have to shield, there's no shieldstun, and Pichu can easily intercept with utilt or Discharge.
Normally, a counter-strategy requires some form of commitment. A player can dodge, jump over, or counter Wario's bair, but they have to commit to that before bair starts. Then Wario can read those options and do something else. Dodging, jumping, or countering restricts the other player's options, allowing Wario to punish them.
On the other hand, standing still requires exactly zero commitment. By standing still, Pichu keeps all its options open, while shutting down one of Wario's better options. Alternatively, Pichu could dash-dance, which would open up a bunch more options, though it would also make it harder to respond with utilt.