Maybe it's just the Rosalina's I've played, but I think it's way closer of a match up than some of you are giving it credit for.
I find that Toon Link's projectiles do a good job keeping Luma in place, so it doesn't give me too much trouble. Because Rosalina is a bigger character, she's not too difficult for me to zone, with or without Luma. When Rosalina starts getting too greedy with grabbing my projectiles, I'll usually hold a bomb until it's about to explode before sending it her way, so be careful with her Down B. I mostly rely on Fairs for my K.O.s in this match up. Because she is so light Toon Link's Fair will K.O. earlier than other characters, so be wary of that. Same with his Up Air. That being said, Rosalina definitely beats Toon Link in aerial combat. Both her Up Air and Down Air pretty much out prioritize anything Toon Link can do while killing him early, and her Fair and Bair have a lot of range. Her Smashes are a good way to get Toon Link out if he gets a little too comfortable up close, and they're good for guarding the ledge along with Luma as he's trying to recover. Also be aware that both characters have good tactics for ledge guarding in this match up. Toon Link's projectiles and Dair spike, and Rosalina's Smashes and safer Dair spike. On Battlefield Rosalina can give Toon Link quite a bit of trouble as her attacks can reach above her head and through the lower platforms so those areas aren't too safe for him, but Smashvill will give Toon Link a little more space to get around.
On personal experience alone I would rate this match up at about 52/48 in Toon Link's favor, but I definitely won't deny that a good Rosalina can be very troubling for a Toon Link main. It's pretty even in my opinion.