Don't take Vergeben too seriously. He's gotten a few things right, both with Smash Ultimate and with other games, but has definitely gotten plenty wrong. I don't put much into him guessing Ridley at E3, because I guessed the same thing would happen. No cuts from Smash 4 wasn't a hard guess, either. Snake coming back was a risky call, but was never impossible. And if you're going to guess Snake, Simon Belmont isn't far behind. It seems to me that he managed to guess some stuff right, and is trying to keep this going as long as possible.
It seems to me like whenever some time has passed without himself being talked about, he says something new to bring back the spotlight. Such as saying any leak without Simon or Isabelle is false, saying certain characters won't make it in, etc. Vergeben holds back info, uses vague descriptions, and tries to falsify other leaks. It sounds to me that he wants all the attention on himself, and I think it's only a matter of time before his lust for attention causes him to slip up.
Don't lose hope on Decidueye, no matter what some random on the internet says.