Well, strictly speaking, there are plenty of ways to change Sheik's abilities around, all the while keeping her fast, safe ninja persona intact, but at least pulling in the reins a bit so she's lined up with Rosalina and ZSS and the like in terms of viability. There are a few obvious ones that I'm sure everyone's thought of at this point, as well as a few that might not be immediately evident. Of course, I'm not suggesting that ALL of them would need to be applied to achieve the desired effect (in fact I would think that would be unreasonable), but it's just a brainstorm, after all.
Hopefully I'm not put to the fire with over 9000 slaps and needles for this:
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- Aerials
Just for the record, when I mention aerials, I'm referring to it as a blanket term for Fair, Nair, and Bair combined. Usually, when most people think about how these should be nerfed, the first answer that comes up is "increased landing lag." And while that would be a desirable change for non-Sheik players, a change like that really would go against what the character of Sheik stands for. In this case, I wholeheartedly agree with the OP in that what should be changed is the incredible amount of range and disjoint these moves are sporting. They already have amazing frame data and really consistent damage off a stray hit, but when you add the reach of these moves into the equation, they start to become incredible moves that can take the neutral by force in a huge amount of matchups.
I'm sure we all know the story here. Spaced Sheik aerials are 100% unpunishable by almost the entire cast, and even on a powershield in most cases, and spacing these moves is incredibly easy due to their natural disjoint. Thus, what needs to change is either the speed or range of the moves. Since we all understand that messing with Sheik's speed would simply be taking away from her character design, it's the range that should probably be touched up. Sheik is not a character who should have any disjoint on her moves at all, really. It's still important to reward players for spacing their moves properly, but it definitely shouldn't come as easily as it does right now for Sheik.
- Needle Storm
A lot of people suggest an ending lag increase to this move, and that's certainly reasonable, as punishing Sheik from midrange and even close range for a lot of characters is close to impossible. Adjusting the ending lag makes more sense in this move's case because the sheer speed of Sheik's character shines through in the needles themselves, rather than the frame data of it all.
However, I'm not a hundred percent sure about that kind of a change. As many Sheiks have mentioned, messing around with the frame data on needles could potentially screw with some of her gameplan, with the most commonly cited being full hop needles and aerial needles > Bouncing Fish. At the same time, though, leaving needles as they are with that kind of frame data is dangerous, because it allows Sheik to pressure opponents from afar just by existing. The needles are not just really fast and almost impossible to punish, but also provide huge benefits when they hit; popping opponents into the air and making it effectively impossible for them to land as more needles come. My proposed change to address this but still keep the overall utility of the move might be a little controversial, but how about this: "The grounded version of Needle Storm cannot launch opponents." Think Falco Lasers, but with a bit more hitstun.
With that kind of change, all of Sheik's aerial needle gambits are kept intact, and she still retains her ability to quickly stuff opponents on the ground trying to set up any tricks from afar. However, what does change is that she doesn't suddenly gain an advantaged state from hitting the opponent with a maddeningly fast projectile all the way from the other side of the screen. As a result, it doesn't force the opponent into this convoluted dance that doesn't even make any progress in the match if one wishes to circumvent these needles.
- Down Throw
This point is fairly obvious, but Dthrow should be adjusted so it doesn't lead into that ridiculous guaranteed kill or 50/50 guessing game starting at 110% or so. The easiest way here being to increase the knockback growth on Dthrow. In Smash 4, it's really obvious that Sheik was meant to be marketed as a character that has a hard time killing. And for the most part, she does, with the exception of her patented Dthrow Uair combo, or fake out into Vanish, both of which can close out stocks at unbelievably low for an allegedly "weak" character. And keep in mind, all of this starts from a grab with some seriously good frame data. If we want to talk about keeping a character in line with their design goals, this is one of the points that should more urgently be addressed.
- Vanish
I'm not sure how much Vanish actually needs to be touched, but removing the i-frames would make sense on a design level just on the premise that Sheik in Melee and Brawl has been a character who had difficulties getting back onstage(primarily because teleport recoveries were easily edgehoggable). I'm not sure if it was intended for Sheik to be really good at recovering in this game because of the addition of Bouncing Fish, but Vanish was made to be an infinitely more powerful recovery move because of the new ledge mechanics. You get invincibility frames, followed by a hitbox that can kill, followed by more invincibility frames for grabbing the edge which more or less can't be stopped. Seems like a jarring change from what we're used to in the previous games.
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Once again, before you guys come at me with pitchforks, keep in mind that I do not believe that ALL of these changes should be in effect. In fact, I only believe two or even one change would be required to put her in line with the other top tiers and ultimately keep her top tier. IMO the changes to Needle Storm and Down Throw as explained above would be enough, as an aside.
And that's not even factoring in the buffs I think Sheik should receive, too!
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- Buffs for Sheik!?
If there's anything to pull from everything I just got through explaining, it's that Sheik does have a really hard time killing. And some of her kill moves just don't work the way they should, and seem somewhat dysfunctional. And if we were to take away Dthrow Uair as a kill option, it gets even worse for her. We should do something about that. For the most part, Fsmash, Dsmash, and Bair are the key moves that need to be addressed.
For all three of these moves, they should all have their knockback growth increased by some amount. Enough that they kill at reasonably middling percents, but nothing too extravagant, of course. Fsmash should be adjusted so that if the first hit connects, the opponent gets nailed by the second hit instead of them falling out 90% of the time like they do right now. Lastly, Dsmash's hitboxes really need to be fixed, because right now, it's a whirlwind of... absolutely nothing. I would say just go back to the hitboxes Brawl Dsmash had. Nice and big, right at the startup of the move.
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Anyway, that's basically everything I wanted to say. Keep in mind that I don't believe that Sheik really needs to be touched too heavily, and that only a scant amount of the changes I've suggested really need to take effect in order to make her a Top Tier character that people won't complain about. At the end of the day, though, the Sheik boards are correct in saying that she is a very fragile character in terms of the balance of the game, and that even one wrong change could be enough to rocket her down to Mid Tier. I don't think these are changes that are necessarily going to happen, but would definitely make sense from a design standpoint.
All that aside, in all likelihood the devs are probably just going to reduce the knockback growth on Uair and call it a day, eh heh...
*gets stabbed with all the pitchforks*
*ALL OF THEM*
