quality over quantity. veterans haven't been updated in forever, so I'd like to see them be brought up to par with newcomers.
Most veterans have actually been significantly reworked by either Smash 4 or Ultimate.
Some examples off the top of my head:
-Mr. Game & Watch is basically a completely different character from his Melee/Brawl version. He has like four moves that are still the same
-3 of Pit's 4 special moves are completely different compared to Brawl
-Mario was not a flashy combo-oriented character before Smash 4. To add to that, Dr. Mario wasn't actually slower than Mario in Melee
-All of Bowser's animations have been remade from scratch
-Luigi got the Poltergust and a ton of animation changes
-Link is now BotW styled, he shoots his laser when he's at 0%, has the Remote Bombs, can pick up his own arrows and has lost the Hookshot; this in turn also made Young Link more unique
-DK finally has his roll and can finally use his down B in mid-air, plus he has a ton more facial expressions
-Pokémon Trainer lost the dumb stamina and type weaknesses mechanics; one special and a quite a few normals of Charizard have been changed, Squirtle and Ivysaur play mostly the same but they have both been remade from scratch
-Lucario's aura gimmick has been heavily enhanced since Brawl, his special moves change more dramatically and the difference in power from base Lucario to fully charged Lucario is bigger than ever
-Dedede's side B changed in Smash 4, and his neutral B acquired new functionalities in Ultimate as it can now reflect projectiles, which also combines with his new side B, giving him just so much more stuff to do compared to his Brawl incarnation
-Shulk's Arts last way less and are way more powerful in Ultimate
-Pichu went from joke character to legit glass cannon
-Roy's stats changed dramatically as well as quite a few of his normals, and he actually uses his reverse grip now
-Zelda got radically redesigned and reanimated in Ultimate, Phantom Slash does a lot to improve her playstyle
-Wario lost his jerky animations from Brawl and moved his shoulder bash to dash attack
-Sheik got two new special moves that really bring her kit together
-Falco is barely a clone anymore, and Wolf got completely remade in Ultimate
-Ness's PSI Magnet has a hitbox now, he got new animations and his PK Thunder is more functional now
-Lucas's z-air used to be a useless move in Brawl and is now an important part of his kit that further differentiates him from Ness in combos and recovery
-Jigglypuff got her modern design in Smash 4
-Ganondorf is still the most egregious example of a clone, but now he and Falcon actually share basically just the specials and the aerials
-Yoshi changed posture from Brawl to Ultimate and a lot of his headbutt attacks have become kicks
-Diddy stretches more and has more range, he doesn't use his tail to attack anymore, his dash attack has changed to become a better combo starter, banana has been nerfed, and as of Ultimate he has quite a few new animations involving his hat
-A ton of stuff changed about Olimar. Pikmin order, up B, max number of pikmin, and he has more non-pikmin moves now. Also, pikmin can bring items to Olimar now
-Ice Climbers got a ton of new animations, a few moves work differently, they don't have the chain grabs anymore
-Kirby by definition gets updated each time they add a new character
...Sorry. This got way longer than I thought it would
But I mean... Saying that the veterans haven't been updated in forever feels ungenerous to me. How are these not significant changes? Some of these might not be the flashiest freshest things ever, but they're enough to change (or to improve) the feel of a character. In fact, I'd argue that almost every character feels at their all-time most distinct and functional in Ultimate.
Balancing is also the best it's ever been, despite the gigantic cast. Not that it matters to 90% of the player base, but even low tiers quite often have crazy tournament runs and I believe most (if not every single one) characters have gotten top 8 at majors?
Super meters and crazy gimmicks get a lot of attention but it's not like every new character has those. Ridley, Simon, K. Rool, Isabelle, Incineroar, Plant, Banjo, Byleth, Pyra/Mythra and Sora aren't really more intricate at a superficial level than the average Brawl character. That's half of the newcomers.
A few models are admittedly starting to show their age (looking at you Diddy) if you pause the game and zoom, and you can always make some adjustments, but again, I really can't see in what way exactly the newcomers are of such a high quality to obscure the veterans.