Dude. You’re just wrong about this. K. Rool, Ridley, Geno, and Banjo have all been the huge requests since the original game. But beyond their popularity within the community, they were all united because their inclusion was thought to be impossible for one reason or another. It shouldn’t really be “the big four”. It should be “the impossible four”.
The
original game? Wow. You, my friend, are
waaaaay off base.
Let's go in the order you listed.
K. Rool: obviously took a backseat demand-wise to Diddy, who was a front-runner for both Melee and Brawl. K. Rool's popularity didn't rise until the latter days of Brawl, after Diddy had already been included. Then, once again with Smash 4, Dixie surpassed K. Rool for several months in anticipation when people caught on that recent appearances were what was being prioritized. K. Rool returned to overtake Dixie during the ballot. He is actually the newest of the four to have leading popularity, and was the most sustained.
Ridley: Ridley does have notable popularity dating the furthest back, to Melee. Well, of the popularity that was sustained. However, back then, Ridley was just one of many voices in a crowd. He was not leading the pack. Keep in mind there had only been three Metroid titles, and none since the SNES, while, according to ChronoBound (who has been around since pre-Melee) characters such as Bowser, Peach, Wario, Diddy Kong, Ganondorf, Zelda, Sheik, King Dedede, Mewtwo, Meowth, Charizard, and Banjo-Kazooie dominated discussion. After Melee was revealed, to quote ChronoBound, Ridley was then within the top ten, though not top five. This was in part thanks to Melee's opening having raised expectations for him, Wolf, and Goroh. But even leading up to Brawl he was simply just one of many front-runners in a crowded race. After Sakurai's late Smash 4-era statement that Ridley was basically infeasible, expectations took a nose dive. Hence why everyone was very skeptical upon the first Ridley in Ultimate rumours.
Geno: Geno was a cult-favourite dating back fairly early, but he didn't gather the clout to be a front-runner until the lead up to Brawl. Perhaps you'd cite the Melee poll, but keep in mind Geno wasn't even in the top thirty on that thing. Early Nintendo memes such as Geno's Forest or whatever it was called help popularize Geno during the pre-Brawl lead-up. Then during the Brawl cycle when people misinterpreted the quantity of mentions on the Japan-only section of the DOJO, Geno's four mentions were inferred as actually being tied for second on the poll, which wasn't the case, as the poll has never been released (though it has been confirmed that Mega Man was the second-most requested third-party, Sonic being first). But by then Geno popularity was in full swing. However, after Brawl, Geno's popularity took a plunge (from all the ballot exit polls, it seems like he wasn't in the top 10), which only resurged when both his costume and the statement Sakurai had considered him for Brawl were revealed.
Banjo: Banjo is the only character who genuinely would've been a front-runner since the original game. He was at his height then, and during pre-Melee. However, once Rare was bought out and made exclusives to the Xbox, the discussion and expectation dried up completely and for thirteen years. He's the only one of the four that was ever actually seen as impossible. Had the other three been seen as actually impossible, they wouldn't have been at the centre of so much expectation over the years. I urge you, go back and survey the discussion from 2003-14 and see how scarcely he's brought up. People wanted him, but a huge request? Absolutely not. He wasn't seen as possible. He didn't even have a thread for Smash 4 until
2015, which then didn't even get a second post in it until the following month, when Spencer's tweet reignited the flame.
Have they all been huge requests? Absolutely. Since the original game? Not a chance. No character has. They've either already been included, or their popularity eventually curtailed. I understand fans like to exaggerate the tenure these characters experienced top-tier popularity, but much of it is untrue.
Keep in mind I can speak both from first-hand experience since from about 2005-06, and from my many talks with
ChronoBound
over the years, who is basically the grandaddy of Smash spec at this point, having followed and kept track of the series since before it even released.