Except the real reason Uprising got a lot was due to the 3DS version being easy to transfer over to from... a 3DS game. And that Dark Pit was more on his team thinking of ideas for an easy clone. It's not really the same situation.
As for Sheik, keep in mind that Zelda and Sheik were a duo who got in due to a very specific gameplay mechanic. They weren't treated as easy separate options. Zelda would've been weird without Sheik too, due to not having any obvious skills to be used for playable. She barely was anything more than a Link clone in previous non-canon games and some media. Sheik was only easy to see working cause she's an archtypal ninja. Zelda can't really say she's an archtypal mage, as she fights with both magic and some attacks that are far more monk-like. Her entire moveset bar Transform and her Grab(and maybe her throws) are awkward and while arguably fun to use, don't really have any clear basis. The reason Sheik's archtype ninja isn't awkward is because we at least can believe she was trained as a ninja by Impa. None of it really sticks out bar at most, what, the chain? The needles make sense. This is also during a time when things like Naruto were about, so it makes even more sense why that archtype is easy to imagine. And even then, Sheik isn't really a Ninjutsu-style ninja(that is, the media depiction, where it's more magical. It's the actual proper name of the fighting style in real life which is physical). Like, the closest thing is Ninja Vanish, and technically Transform. She still takes some similar stances, but at most is closer to Taijutsu media-wise.
But regardless, she's not hard to imagine a simple fighting style. Zelda is all over the place in abilities within the franchise, so making a coherent moveset is obviously going to be harder. It's easy to see why they went with a specific gameplay mechanic. Her having hard-hitting magic makes a lot of sense when for the most part, she's able to seal away evil. So "finishing the enemy" is a pretty reasonable representation of that concept. It's not perfect, but then again, her lack of core abilities nor an obvious archtype didn't help either. In fact, the most we had was she was clearly a Telepathic user and could use something outright to open doors(which could've been magic or psychic abilities, due to inconsistent information throughout the franchise). Sure, it's a different Zelda and all, but we weren't really at the point where there were tons of different ones with unique abilities. WW and TP were the first times Zelda really started to not be a 100% atypical princess with mild mystical abilities at best. Well after Smash. Kind of hard to take from there and all. You only had ALTTP and OOT to go off of, and the fact she does fight in other media(so her being an action girl in any way is at least acceptable instead of just being someone to save. Peach already was playable/taking action far more, so obviously she didn't have the issue as is).