Her original design document was that she would switch between Zelda and Sheik, with Sheik racking up combos and Zelda having strong kill options. As a whole Sakurai hasn't really made drastically huge adjustments to non-clones over the years, giving exceptions to Falco, Luigi, Ganondorf and Young/Toon Link here and there. Hell, Doc as a whole isn't really hugely different beyond some simple basics and he was put on the backburner for this game.
Ultimately, one of the things that wasn't really ever worked out was what happens when Zelda loses that switch option, which is precisely what happened this game. During development it was clear they intended to keep the mechanic, but it was switched because of hardware issues. So what happens when half of your intended arsenal suddenly disappears? She wasn't ever exactly fundamentally adjusted in terms of having something to circumvent the fact that while she has some strong options she lacks the mobility and good buttons that many other characters just have. With Transform in mind, her rather strangely designed kit makes a bit of sense, but now that it's gone it feels very much strange and incomplete because her options were taken away thanks to hardware limitations.
In the end, yes, she does have a few things, but from a design standpoint her completeness was having a second set of skills that ultimately proved to be laughably superior. It's true that she's gotten many a buff, but for her to be really something special, she'd need to recieve a massive overall set of tune-ups or an outright fundamental design change come next game.
I actually don't disagree with this at all and I have seen this for a very long time, now.
In fact, the fact that Zelda is separated from Sheik yet she's still balanced like she's tethered to her and clearly suffering because of it is why (emotionally, not in any practical sense) I went from having Sheik as one of my favourite characters to someone I'm
really on the fence about. As the years went by, I started growing a preference towards Zelda over her, and it does pain me to see the state she is now.
Zelda alone really needs Sheik, Sheik alone doesn't need Zelda. Zelda still can end up killing at even later percents than Sheik so it's not like she could've ever really been used to end stocks with her design. Zelda without Sheik, while after the buffs she can get ridiculous damage output per neutral victory, still doesn't quite rack up damage as well as Sheik does, and has a harder time doing so. Also...
Zelda's neutral is bad, can't approach, force approaches, or defend against approaches as her defensive tools are slow or don't cover enough space. And her advantage state isn't stellar either.
Her grab is as slow as tether grabs but has range slightly above average, and her Dthrow can be DI'd to make it hard, if not impossible to connect (I know being just "hard" is not an issue, but requiring a stepdash is a different level of "hard").
She gets juggled forever due to her floatiness, doesn't have safe landing options, and while Nayru's Love is a good get-out tool, it gets easily baited and punished. And she's pretty light so she'll die early.
Yes, Pamyuu, I know. These are all very real issues, and I acknowledge them.
But as real as they are, those are traits a lot of the Bottom and Low Tiers already share. These are far from exclusive issues of her and it's not even like she's the character that suffers the most out of them from these.
The limbo that is the question "How does Zelda approach or force approaches" is something that is discussed quite frequently even amongst us, and is part of what makes her current moveset feel "incoherent". That's one of the very real weaknesses she has, but again, it's not as if she has no options. She uses the limited tools she has to more or less play bait-and-punish, forcing somebody to commit to something they shouldn't and then punish their lag with a Grab. Her Grab is hard to get but not exactly "You need to step-dash it for it to be usable", that
helps but it's not as if she can't even get out of bed in the morning if you don't do that. I've seen many Zeldas just use the regular grab options and do just
relatively fine with it. Once again, I know the hard to get grabs are a definite weakness, but at least she has quite the respectable grab game once you do land a grab, which the good Zeldas tend to get quite a few of during a match, and that's already more than what can be said about a lot of characters in the Bottom 15.
I am probably really stressing this, but I am at no point wanting to deny the fact that Zelda has very real and crippling weaknesses. I am just saying that, despite those weaknesses, she actually has quite a lot going for her, perhaps more stuff than any of the other Bottom Tiers, and those advantages
do matter enough to be taken into consideration if somebody's wanting to talk about who the worst characters in the game are. Zelda's in that category, but I believe she's not at all the worst one.
If it matters to any capacity, Nairo said he doesn't feel like he's using the worst character in the game when playing her, and in his last tier list he put her on Low Tier instead of Bottom. It's not like his opinion is necessarily right or end all-be all, but at least somebody out there still somewhat sees what I am seeing.