That's not really the whole answer, Baby Daisy instead of Waluigi is only better if you're already good at the game. Using her snaking drifting technique will only save time if you're one of the top speedrunners. Like, I've been doing time trials for hundreds of hours and I'm still not good enough to save time with Baby Daisy.

In multiplayer and online, having low weight is a bad thing in competitive play, as you can easily be bumped into walls or off the track. Most competitive players will use a combo with more speed, Waluigi on Wild Wiggler/Azure Roller/Paper Glider (the same one as the Mario Kart Stadium world record). Since this combo is a heavy one, that makes anyone using a lightweight combo vulnerable to almost everyone.