Okay imma say it again. Any fan poll that ISN'T the ballot is BS because it is simply NOT the ballot. No matter how "likely" it may be, there are a lot of people just like myself that ONLY voted in the ballot, y'know, the one that mattered. This brings me back to my point that those fan polls are for more hardcore fans and not casual ones.
However, if we are to go by history, there was an official Sonic popularity contest many years back and the ranking order was Sonic, Shadow, Tails, Knuckles in that order. In the Smash Bros series, generally being an assist trophy means you're one step away from being a character.
So, if Shadow, being #2, was an assist trophy in Smash 4, then it should be assumed that no other Sonic character would make it into the game. But in Ultimate, Knuckles, the #4 spot, is now the assist trophy. I'm going to state again that it would be REALLY weird if #2 and #3 didn't have more important roles than #4. Unless somehow Knuckles got super popular recently which I doubt.
And it's still kind of a question that if Shadow was by far the highest voted Sonic character. Why did Tails and Knuckles get Mii costumes that have been shown to be consolation prizes/hints toward being playable, keep their already established assist role, or an upgraded role in Smash Ultimate while Shadow did not?
Thing is, Dark Samus did not get a Mii Costume either, rather she was an assist trophy, so that doesn't prevent a character from not making it in the game as a playable character.
I honestly think Shadow scoring higher than Tails is irrelevant, especially if he's going to be an echo. If Fire Emblem can get 7 reps and Castlevania can get 2 reps, and characters that haven't appeared in 10 years can be in the game, I really don't think Sakurai honestly cares about arbitrary numbers anymore, he just wants to put characters fans want into the roster. If Tails and Shadow are both highly requested characters, both of them will get in. Simple as that.