I keep seeing people claiming that the original veterans are in dire need of a moveset update. Looking at their movesets... yeah, I have no clue what makes them say that.
Their movesets are mostly practical and referential to the source material. Their performance isn't too shabby either, as going by Smash 4's tier list, the majority have decent placements on that list.
-Mario has always enjoyed a plethora of moves and power ups from across the history of his series. All his normals and specials are on point.
-Mostly the same with DK. At the time of his debut in Smash, he had about a grand total of three moves to work with: Barrel throw, Hand Slap and his rolling attack.
The first is represented in his Cargo throw, the second one has been there since the beginning and the third one was eventually added in. Giant Punch is more or less based on the ending from DKC2 and Spinning Kong is a reference to Dixie. Headbutt came from nowhere, but DK actually uses head attacks in Jungle Beat. I'll concede that his Coconut Gun may have a place in his moveset but he is fine as he is.
-Link is on point. They got away with changing him though because there are two other Links now that can carry that role.
-Samus's specials are fine and she has been shown capable of CQC as displayed by her normals, but if there was a change I would make is to have her Down Smash be like Mii Gunner and her Jabs be short ranged blasts. Otherwise, mostly good.
-Fox has almost nothing to take from his games so he is fine. And contrary to popular belief, Fox specials are actually based the on the fire and illusory powers of mythical foxes in japanese folklore. As mentioned by Miyamoto, Fox himself was inspired by the fox statues from the Fushimi Inari shrine.
-Yoshi is perfect.
-And so is Pikachu. Like Yoshi, its toolkit meshes really well. Just because there are new Pokemon moves it doesn't mean that they should fix what is not broken. Volt Tackle as the FS should stay because its the signature move of the Pikachu line.
-Kirby's moveset is faithful, but I would agree with some that his specials need to be tuned to become more effective.
That's subjective. I feel like a lot of these could use reworks.
A few examples:
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Should step out of the clown car and actually use his paintbrush and other weapons from his boss appearences
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and
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should have their moves changed to match their games more instead of being portrayed as big primal screeching monsters
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and
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could probably be decloned
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and
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should use the items unique to their games or items that first appeared in their games instead of the traditional Zelda ones (because that's redundant). Young Link should also use the slingshot, but that's a personal preference.
I don't understand why Jr. should be downgraded by using a moveset based on an early appearance. And his current moveset uses a lot of weapons already, he is like a swiss knife. Giving him the Klown Kar from the New Super Mario Bros. series was a good idea to make him stand out.
And I don't understand the changes you are talking about for DK and Bowser. I played DK Tropical Freeze, and nothing there was notable enough to be used as a new move for DK. He still rolls, he still throws things, he still punches and he still hand slaps; just like in Smash and the old DKC games. They even updated his FS.
Same with Bowser, his moveset captures the brutality of his character. He more or less brings in a new gimmick on each Mario game but the essentials remain unchanged. He can stomp, breathe fire, swipe or punch.
With the other two Links, they are almost perfectly faithful to how they fight in their home series and perform well enough to sometimes even outshine Link. 3D Zelda games share an abundant amount of common moves and weapons. Their sword slashes, spin attack and items are consistent with how they've worked in those games. Those items you speak of tend to be a one time gimmick unique to the game they first appear in. For instance, is not necessary to sacrifice Toon Link's Spin Attack for a Deku Leaf recovery.
I don't understand some of the other examples you suggest. How would Captain Falcon, Fox, Wolf and Falco be updated? And a better question: why should they?
From what non existing canon material would Falcon pull from? Same goes for Fox, Wolf and Falco. And no, turning them into artillery based fighters like in the walking sections of Star Fox Assault would be too jarring at this point.
And Olimar? What exactly is wrong with him now?
And Lucas? Megaman? Pacman? ZSS? Robin? Frickin' Ken?
At least elaborate on what is wrong about them that warrants to be updated. As I said before, there is no need to fix what is not broken.