I've considered this too. Kamiya and Sakurai probably shoot tequila shots on the weekends but the timing is still off. My big issue isn't just the timing of Kamiya's poll, it's Sakurai saying that the doors of the Fighter's Pass were shut and locked like a month and a half before it. Sakurai literally took to Twitter (in English no less) said "yo, uh... S'up fools? We've already decided the Fighter's Pass so, uh, don't bug us with fan campaigns, aight?" They knew who they wanted, at least the first 5. We have decent evidence that December 2018 was when existential dread started to wash over Sakurai and he thought "****... The Smash fanbase isn't just going to be satisfied with these 5 characters, are they? Goddamnit... GODDAMNIT! *sobs*" Like I outlined, I feel like we have a lot of clues for who Sakurai immediately thought of when he was like "ah **** on toast, I have to make a Season 2, don't I?"
So, like I showed, Kamiya's poll was mid December so what probably happened was that Sakurai knew he wanted "une bebe du Kamiya" for Season 2 and asked his bro who he wanted to add. Said honorary bro then took to Twitter to ask the fans. Dante won overwhelmingly. "Well, ****... There's no DMC games on Nintendo platforms... Let's fix that!" Fast forward to February and Capcom makes an official statement on it saying, and I quote, "Dante can get into Smash if you smelly nerds push for and buy DMC games on Switch." The fanbase obliged. DMC for the Switch came out in June. Now, from an analytical point of view, games usually sell their best their first two weeks and drop off significantly from there. It was a port of an 18 year old game; I can't imagine it did super well, let alone impressive enough to spur the automatic greenlight for Dante in Smash. This is why I don't believe he was greenlit yet when his rumors first came about.
Time has gone on, more games are coming but this was probably always part of the plan. My personal theory is that Dante was probably fully greenlit very recently. The campaign worked to a satisfying degree, "let's get the ****** in Smash." Ironically, I think he's ahead of schedule. The sales of the first two games and interest in the collection were probably enough to tell Sakurai and Kamiya, "yep, Nintendo fans will definitely eat this **** up" and why, again, my current theory is he'll either be the last character of Season 2 or the first character of the Final Season: Sakurai's ****ing Tired.