The thing is, Smash Ultimate has completely failed to do any of that. Fine tuning the gamefeel? Have you even played this game? It feels substantially worse than 4 and there is a horrible "hold buffer" system in place in a misguided attempt to make short hop aerials easier for people, the cost of which is making the game feel much laggier and worse than the last game. The game only performs actions on the first actionable frame if you hold the inputs down, at which point it will attempt to do them all at once, resulting in consistent, repeated incidents of inputting the wrong attack, or getting NO attack at all where you wanted one. The netcode is also FAR AND AWAY much worse than SSB4's, which I didn't think was possible, made all the more insulting by the fact that you have to pay for it.
Smash Ultimate hasn't fine tuned or refined anything, if anything it's taken huge leaps backwards, which may or may not be a result of them taking a quantity-over-quality approach with the content, and serves as another argument for finally remaking the game.
Characters are the most important part of the game? I disagree. Yes, they are important, but what's more important is having good controls, good online, and nuanced gameplay with the potential for depth. It's lacking in all these areas.