Wario's never been a darker character. He's alway had goofiness baked into his character. During his conception Kiyotake even compared Mario and Wario to Popeye and Bluto. He's a cartoon character, always has been. The kind who will toss buckets on people's heads for his eeeeevil scheme.
He has a more fleshed out personality than most of the cast, sure, but a lot of that comes from the fact he ISN'T this inhumanly cruel monster. He's a thuggish, greedy treasure hunter, a game company CEO who when at home, is decently chill if you don't stand in the way of his interests and a spiteful Mario rival. He can be all that and even more.
It's no different from how Bowser can try to create a whole new galaxy of his own to rule one day, genuinely trying to kill Mario in the process, only to be his Tennis doubles partner the next day or how Rosalina partakes in the goofiness of series, even at her own expense, despite having a somber backstory. The cast is made to be flexible and function more like old-school cartoon and comics characters, a comparison Miyamoto himself made and Wario follows suit.
I DO think he could stand to get some of his more thuggish traits back. Wario's vices and negative qualities are a important part of who he is and I do think he can sometimes be made too much of a gag character. Move It being the worst example, where he is softened so much his abuse and humiliation doesn't even feel earned.
