I have been summoned by
Luigifan18
and I must answer...
Personally, I see far less problems in this game specifically when it comes to character viability, however that could easily be due to no one having the true meta down right now.
Something people overlook a lot is that the balance of characters is not in a vacuum. That is to say that the characters themselves aren't the only things that cause imbalance. And no, it's not even matchups either, because that still constitutes fighter characteristics.
We also need to think about the general mechanics that the game has too. In Ultimate, it would seem that a lot of the universal changes favor aerial to ground pressure, high shield pressure safety, the ability to punish jump out of shield, and the ability to keep advantage by baiting out airdodges. Now that we have noted this, it seems like characters that have very quick, spammable aerials will be really good and characters with poor disadvantage or a lack of ability to regain neutral will be worse.
I think some of these early impressions stem from these observations. To change your fighters, you must first understand what environment they are getting themselves into. For examples with past Smash games, in Melee, shield pressure and baiting tactics are key along with tech chase ability, so fast characters reigned mostly because slower characters couldn't keep up with what the game mechanics entailed. For Brawl, it was mostly about camping and chaingrabs, so the bad characters in Brawl were usually the ones who didn't have these traits as much as the top tiers.
So what do we do about this? Well, we need to make sure we know what meta our environment COULD grow into, but this takes time. But after we understand it, we then nerf the super top tiers and buff the low tiers. But since we need to keep character identity and weaknesses, this can be a bit difficult, but not impossible.
In Ultimate specifically, if my conclusions are right, then the bottom tier characters will be those with poor disadvantage states, and you will either need to make them better at escaping it, or not change that, but compensate for it with making their strengths more attuned to the metagame's needs of them (in Ultimate's case, good aerial to ground pressure and ability to cover options).
Where we are now is the testing phase, understanding what this game's mechanics are trying to generally motivate out of the players. After we figure it out fully, only then can we really see where the characters stand up.