Donkey Kong arcade has the King of Kong documentary film and of course is one of the unfortunate faces of the rather piss poor Pixels. DKC has yet to make the silver screen. Donkey Kong arcade has had multiple Simpsons reference. DKC none. In terms of general public awareness the arcade games are still bigger than DKC. Can't compete with that level of popular culture.
and DKC wasn't sullied by being in Pixels,
check and mate
I still think, especially given how Sakurai himself sees Smash's audience skewing towards younger players, someone like Dixie and Cranky (I will admit K. Rool probably means jack all to a kid who grew up on the GCN and/or Wii) is going to be immediately more recognizable than Jr. to most of the Smash audience. Jr. is more like Duck Hunt than Little Mac; absolutely a beloved retro character, but unlike Mac while he's not the most obscure character ever, I think calling them an 'icon' in today's day and age feels like a stretch. Punch-Out on the other hand despite relative obscurity in modern-Japan from my perspective was always considered one of the big defining games of the NES in the US and had fucking Mike Tyson headline a game. Like the original Donkey Kong is enormous even today, but
that's not the game Jr. came from, and he doesn't seem to live on in pop-culture the same way Punch-Out/Little Mac did. Not that Dixie's is anywhere near 'iconic' mind you, but she's recognizable to younger Nintendo fans and 'relevant' to her own franchise still, which were obviously big factors behind lot of Smash 4's newcomers get in.
Also it's worth pointing out the original Donkey Kong game has already had its two main characters playable since the first Smash, the main item of DK arcade has been the most powerful item in Smash since day one and the series in general pretty regularly talks about the arcade games. It's not like Wario Land where Smash awkwardly ignores half a franchises' existence and there's this weird big gap in the character's history as a result; it's been regularly referenced and featured from SSB through to Smash 4.
Kinda aside since replaying DK'94 recently reminded me how weird Mario vs Doneky Kong's direction was, but calling anything after the first game a continuation of the arcade-style DK feels disingenuous; the sequels have little to do with anything in the original Donkey Kong arcade games beyond the hammer items and Pauline cameos.