You're both right to an extent, but Golden... the All-Star Event Matches? You don't believe that Sakurai thinks that Captain Falcon is a Legend of Zelda character, do you? Samus is a Star Fox character? Ness and Kirby are Pokemon characters? The All-Star matches are simple groupings of characters, nothing definitive. Also, I don't think Sakurai really recognized Wario as a part of his own series until WarioWare, for some, strange reason. Maybe he just wasn't overly familiar with Wario Land, or he considered it still quite similar to Mario.
I won't argue that they aren't considered Mario-related characters, because obviously, they are, but if you want to get real technical about it, each character does have its own series, whether the series is still basically Mario or not.
That being said, anymore characters that we see from either the Donkey Kong series or the WarioWare/Land series would not be considered "Mario characters." Dixie, King K. Rool, Captain Syrup, and Mona are not Mario characters. Donkey Kong, Yoshi, and Wario are kind of on that thin-line where they can be considered both Mario characters (although not technically) and characters representing their own series. This is also why Yoshi will not get any newcomers ever (unless a new great game with tons of popular and interesting characters is released). It's too closely related to Mario, unlike Wario and Donkey Kong.
So... my point is, Donkey Kong, Wario, and Yoshi can be onsidered "Mario" characters when convenient, but other characters from their series (besides Yoshi) would NOT be considered Mario newcomers. The only other Mario newcomers we can see are from the ACTUAL Super Mario series.