Yeah, I really don't see your reasoning.
He's a one-off boss character. He's not even the final boss. He was pretty heavily promoted, sure, and he's fun to fight and has a lot of personality, but there's absolutely no precedent for a character like that, from
any series, getting into Smash Bros. There are only two Smash characters who have only been in one game from their franchise, and that's Ness and Lucas. And they were the main protagonists of the games they appeared in. Ghirahim is not an "all star". Not even within the Zelda franchise. He's just one of a handful of interesting characters from the most recent 3D game that the community has latched onto ever since he appeared in the very first (fake) Smash 4 leak. A character of equivalent stature in the Mario series would be Dimentio or Fawful, and you never see leaks with them playable, because even "leakers" acknowledge that would be absurd.
Say what you like about Tingle, but he's iconic, and was at one point popular enough in some parts of the world to have his own series, making him much more of an "all star" than pretty much every Zelda character that isn't already in Smash. Give it time, and after the next 3D Zelda comes out, there will be another fan favorite side character people think is gonna be in Smash, and most people will forget all about Ghirahim the same way they forgot about Midna and Zant after neither of those characters showed up in Brawl. Ghirahim is fabulous though, I'll give him that. But if people are that eager for a colorful, flamboyant, somewhat rapey Zelda character, I know just the man.
Tingle would be awesome.
We need more Tingle leaks.
Here, here. That's why the Katakana leak is my favorite so far. It had Tingle.
