I did.
But Mario is missing a ton of major characters.
Toad, Toadette, Waluigi, Paper Mario, King Boo, and of course Geno.
I wouldn't really call those 'major' characters.
Toad is the closest and he's represented in Peach & Daisy's moveset (though I think Toadette should have been used in Daisy's instead of Blue Toad). I also feel Toadette would be a costume for Toad and that neither of them would really offer much moveset-wise that isn't already covered by Peach or Mario/Luigi.
Waluigi is a side character in spin-off titles..even though I feel like he should have been added to the Wario series ages ago..but not exactly a 'major' character..I mean, Nintendo even left him out of Mario Kart 7..as dumb as that was.
Paper Mario would be fun moveset-wise, though he's still a side-series character and is, essentially, just Mario character-wise, so not really a major character (but one that would be quite fun).
King Boo is one I'd love since I adore the Luigi's Mansion series, he'd be a fun character, definitely, though still not a major character..Nintendo can't even seem to use THE King Boo in their spin-off games..they keep using generic Boo in a Crown and calling it King Boo..It wasn't until Mario Kart Tour that King Boo from Luigi's Mansion was actually used in something else (and it annoys me how they keep using that generic Boo with a Crown..gimme the real King Boo!)
Geno is far from Major. He appeared as a primary character, yes, but in a spin-off game where he had only 1 notable appearance, being said game. Super Mario RPG is the best Mario game (or at least my favorite) but Geno isn't a Major Mario Character.
Not against the characters appearing at all, in fact, I'm a fan of each of them (the only Mario character I hate is Bowser Jr..but I accept his inclusion in Smash due to his major character status..)..its just that, aside from Toad and maybe King Boo, none of them are really major characters..heck, Toadette only had appearances in spin-offs and cameos in main series games until she appeared in Super Mario Bros. U Deluxe.
I also fear that Sakurai only wants to pull from the main series (or that its some sort of mandate from Miyamoto..I mean, the man did demand all original characters in Paper Mario be replaced by generic main series characters..I could see him demanding the same from the Smash Bros. roster of playable Mario characters..so for all we know, any series Miyamoto is in charge of could be why we don't get newcomers from them..but that's just speculation due to how Miyamoto acts with the Mario series half the time these days..)