Pit's hitboxes are awful, yeah. Most characters have hitboxes to the side of their upsmash so you can hit people diagonally above you and people who fall past you. Additionally, many characters tend to have "connecting" hitboxes in between swipes to help keep the opponent inside the moves whilst the multiple hits connect. Not Pit though. His upsmash only hits directly above him, so run-up upsmash sucks and it's hard to hit characters with good aerial drift (like Ness). It and nair also don't have the sort of hitboxes that keep people inside of them so you can even airdodge through or fall out sometimes. Pit is fun, but this sort of shit gets old real fast.