Except not really. There's a total of 7 Mario Universe characters. Those are all separate universes, although the fact they're remotely related may be partially why we don't see many of the other universe characters.
Gen VIII doesn't even exist, so that's a gross exaggeration too. Spring Man is way more guaranteed in comparison because he not only exists, but is an extremely successful IP.
Nope, would be way too many. Smash isn't like other fighting games. It has a director who cares about series representation. It's absolutely unfair to go that far. 8 Pokemon is huge, and a pretty reasonable cut off point. Adding more than one newcomer per game just creates a balancing nightmare. No other series has remotely hit more than 7 at any point in time, and alternate costumes do not count. The only thing that counts is exact symbols for the purpose of how the game is designed. And even if you count Yoshi(who admittedly is being treated the same as a Mario universe character in the roster design), that's still a max of 8. Keep in mind Mario was meant to have 6, not 7, anyway. Sakurai even noted how he thought giving Fire Emblem a 6th character might've been too much, which is why he was hesitant on Corrin. Uniqueness and timing(as it was now or never) won that round, due to his team convincing him.
There's seriously no reason to give any single series 10 characters alone when it's not just uncalled for, but it vastly undermines other series that really do need a bit more at this point. Mario and Pokemon have been fairly close in amount of characters, with no more than 2 per difference. They're the biggest franchises. Just because Pokemon have quite a few candidates doesn't mean they should overdo it on the franchise either. 8 is pretty huge for any single series as is, after all. And again, I must note balancing and you can't have that huge of a roster without making it too much as is. It's not just a nightmare to balance, but it's also a pain in the *** to go through Classic/etc. with everyone(and that's not just because Classic has gotten really boring since Brawl, with few unique mini-games at all) as is, as it's tedious. There's a thing called "too much". Making a series balance(which Sakurai has touched upon, and actually a fairly big reason why many believe he isn't going to add more than one 3rd party per franchise proper, due to them being extremely special additions) is very important in building a roster. You just can't add add add. It's way more complicated than that. I wouldn't expect must beyond 70 for a new game at this point, and that's stretching it. That's assuming no cuts too. Smash 4 even had some characters missing people expected. Add the cuts from Brawl, and it becomes even more severely huge. That includes 2 more Pokemon(for a grand total of 8), Wolf, Ice Climbers(who weren't possible with the 3DS, and may not have been possible with the Wii U either), Snake(who admittedly had a lot going against him due to the Konami/Kojima fallout, which was pretty bad timing for development to license him, and that's not counting any other possible factors. As pointed out, Sonic didn't just get back in, Nintendo had to make a deal to get 3 exclusive games before they would play ball, as silly as it was to do so. But it's not like Sakurai had that much control).