Actually Pit keeping his Brawl specials would have been fine, espesically since he lost his SSB4 Final Smash. The Three Sacred Treasures have been importantn in every Kid Icarus game, including Uprising, and I don't think Pit has to exclusively cater to only his Uprising appearance. Mario still uses a Cape from a game from 1991, and the FLUDD has long stopped being relevant in main Mario games. Zelda and Ganondorf are aesthetically based on old game's designs instead of BotW or Skyward Sword, and when was the last Zelda game to feature Din, Nayru, and Farore's gifts?
I see no reason Mirror Shield and Wings of Icarus couldn't have been featured for Pit's standard specials, while Palutena, Dark Pit, the Magnus Assist Trophy, the Uprising music and stage would have been more than enough to refer to Uprising. Also, I just prefer Pit as he played in Brawl. He took a huge nosedive with 4's changes.
Before Smash 4 and Uprising Pit was only based on one game due to extreme limits to what he could do while being modernized, with Uprising he was given personality and an army of things that could make up a moveset. It would be weird for Sakurai to have his vision of Pit not play the way he does now. Plus, having everyone/place/song/thing from Kid Icarus apart of Smash all represent Uprising (including the also revamped/rebooted Palutena) and leave Pit to stay old school is silly (unlike every other series in Smash, they can’t just have one person with a modern voice and personality who prefers fighting in the modern times stay completely old school.
Als, you may prefer his Brawl moveset, but his Smash 4/Ultimate moveset is better for the long run. Only problem with his 4 moveset was his lack in KO power, but with Ultimate he fights faster and can KO opponents better (which has already been shown throughout the Smash Ultimate demo footage of him so far)
Besides, every character who gets a recent game is given some sort of update (
have been given redesigns and atheistic changes to their bodies and gear to match up with a recent game,
finally speaks English,
have changes to their voices and gear to match with with a recent game,
got changed from TP to ALITP to match up with her fighting style and still have a recent touch to her, and so on so forth). Unlike Pit, Mario didn't/doesn’t need a massive overload in his character sine he does the same thing no matter what. FLUDD, the Cape, and Cappy are all only one time things/characters that Mario needed to accomplish his usual Bowser things