My take on the Mario characterizations is I really don't mind them for the most part. I'm okay with them being further exaggerated or iterated on for Smash - we see these characters so often, it's kind of fun to see more extreme or competitive takes on them. And their characterization isn't the most consistent even throughout their own games. Mario does get angry and competitive, we've seen it in games like Mario Strikers. Luigi does cower at unfamiliar and sometimes comedically unthreatening enemies... mostly in the M&L RPGs, and of course Luigi's Mansion. They are flexible characters in how far you can push them and Smash simply chooses to push them in the furthest possible direction. I don't think that's inherently a wrong choice.
I do think Bowser could use another pass though. Moveset wise I'm pretty satisfied with him, just in terms of how he emotes, taunts, celebrates... unlike the other Mario characters, what is in my opinion his most bold characteristic trait is not present. Mario is capable and determined. Luigi is the sillier, timid brother. Peach is dainty, with a bit of attitude (Smash was ahead of the curve on that). When I think of Bowser, I think of how brash he is. He's a bully more than he is a beast. The differences wouldn't have to be anything too crazy, but Mario got a few upgraded taunts that made all the difference IMO. So just leaning a bit more into Bowser simply being a showy jerk, and ideally letting Kenny James voice him, that'd be enough for me. Because yeah the godzilla noises and some of his awkward taunts don't especially jive with his more on-model upright design and dropkicks.
As for DK, I'm also a little bit ambivalent. I think the more wild flair these characters are given is quite fun, actually. It's brought out some really interesting creative liberties like K. Rool's insane dash animation... how do you even think of that? I love it. I wouldn't mind if they reel them in a bit, maaaaaybe give DK and/or Diddy their real voices. I think the updated DK expressions were at least a good step in the right direction. But like the Mario cast, we see Donkey Kong all the time, acting as he usually does - I'm okay with them letting Smash go full ape. That's just me.
Maybe more people would be okay with this kind of thing if it was more consistent throughout the entire cast. I understand that. With this kind of character attention dealt toward later additions it may feel like some of the older liberties have dated themselves or feel out of place now. Modern additions, notably within Mario like Rosalina and Bowser Jr, are mostly squeaky clean on-brand depictions of those characters. And K. Rool was given a certain amount of creative liberty because he hadn't shown his kingly mug in 10 years. With these in mind I'm really not sure exactly what the correct course of action is, but I will say I think Smash has been paying it mind and making small steps toward a comfortable common ground. Mario's thumbs up taunt and Cappy throw, for example, reflect the upbeat fun-loving spirit that we all love him for. So maybe we'll see them lean further into it.