I agree the wario ware characters shouldn't clash with the land series. They're completely different and it's weird to see characters in one series change into another enviroment cause they are very different. But Captain Syrup would a good playable character as well
Maybe we could have Waluigi as a sort of Murfy in Rayman Legends deal, where he's less of a straight-up P2 and more of a tool to solve puzzles with. Or maybe he could have less strength (like you said, it'd be kind of weird for him to be in a game about strength) but different transformations or better jump height or speed or something. Idk, I just want to give him SOMETHING to do
He could be the ¨brains¨ while Wario is the ¨brawn¨. I think this will make for a great co-op multiplayer opportunity. But then again, as shown in multiple games, especially Master of Disguise, he's already intelligent enough of his own.