"OMG RIDLEY, SAMURAI GOROH AND WOLF CONFIRMED!!!!"
You say this but some of us thought this could happen!
Especially after Zelda (who wasn't confirmed in the initial E3 presentation but was in the trailer prominently) was confirmed as a playable character. It's actually a big reason demand for Wolf and Ridley post-Melee were so large. Lots of "leaks" having Wolf and Ridley playable only further established their popularity. Leaks real and fake both directly effect character popularity. Usually for the good, but sometimes for the bad (see: Chrom being "inevitable" in Smash 4... though it turned around quite a lot for Ultimate).
What happened in Brawl (or even before) times? Something to remark? I'm curious.
I was only a bit apart of pre-Melee speculation. It was pretty linear in what characters people wanted with some oddities of course per personal preference. The most wanted characters were basically anything Zelda related, Bowser, Peach and Mewtwo. After that most people just wanted Dedede, Wario, Diddy or Banjo of the characters that didn't get in Melee. There were odd requests, but it's not as crazy as it is now. But generally those characters were dominant.
As time moved on, wants changed. New characters emerged. The biggest change happened because of the EGM Sonic and Tails "leak" for April Fool's Day. Oh man, that was nutty. After that, so many people SCREAMEEEEDDDD for Sonic. The Sonic demand got even louder after Snake was confirmed in Brawl.
And around that time, the demand for Cloud was insane before most of the community reached a consensus "Cloud would never happen" (which is why it was such a shocking Smash 4 DLC reveal and a big reason it was about as big of a deal to see Cloud in Smash as it was Sonic). I would say for a while in Brawl speculation the demand for Cloud wasn't too far off for the demand for Sonic. But again, it was a short period of time.
I actually think if we got a Cloud leak of some sort like the EGM leak after Brawl came out or some early Smash 4 leak that seemed credible with Cloud in it, the Cloud hype and anticipation for Smash 4 would have rivaled the Sonic hype for Brawl.
This, along with the wide spread assertion that nobody wanted Isabelle. You don't show up in Monster Hunter and Mario Kart as a playable character if you don't have a massive following. People talk about the "bubble" of the Smash Community and people can be deaf to what's outside it and this is the leading example. Did people forget about the Mii costumes too? How Inkling was regularly breaking Top 10 in polls regarding the Smash Ballot? Isabelle regularly making Top 5 favorite Nintendo character in Japanese magazine polls since her creation? All the merch? I feel like you'd have to be in total denial to outright ignore these.
Merch is a big reason not to dismiss Skull Kid. The Majora's Mask is a merch moneymaker, which is a key reason I don't discount the Skull Kid leaks and rumors.