as far as i could tell, most of the characters were better designed when i played last time (feb last year). i don't think it's about the characters that are fine as-is so much as smoothing out the rough edges as they come up.
just from observation, sonic was by far the worst designed. whenever there is a sonic on the screen, the entire game is warped around him regardless of what's actually going on. this lead to some visibly awful situations in free play, including the inability to intentionally 3 vs 1 him effectively, sonic's own teammate getting gang-***** 100% of the time for not being sonic (unless sonic stops you), and a player in the finals (theoretically one of the two best players in the room) not knowing what to do against the character mid-set. sonic is an egregiously awful character design and was consistently soft-banned from free play the entire weekend to keep the game playable. i can't stress enough the intense amount of bad that went into this character. really, what were you thinking.
link was...no. make him bad at literally anything. jesus christ.
DK having a better macro game than captain falcon is sketchy, although that just may be my inexperience vs the character. the character heavily encourages grab > moves until KO, and there's a lot of characters that are polarizing like that but don't have DK's weight or grab range.
squirtle, marth, falcon, fox, falco, wolf, mario, ganon, ike, bowser, samus, wario, etc all seemed fine- for now. as people continue to find holes, they will continue to need revisions.
by far the best part about this game so far is the exclusion of olimar.