I'd like to make a case for ZSS. Initially, I thought that she was being overrated because of her tether grab and hitboxes that pass over the heads of short characters. It wasn't until I took a second look and logged some playtime into her that I realized that these weaknesses aren't as big as they look.
1) Her grab is better mechanically than other tether grabs because it catches some rolls and spotdodges, which makes punishing it a little more difficult since if she uses it in the right situations some of her opponent's defensive options are locked out. It has enough range that it's difficult to just beat with a jab. In the corner against ZSS, it's often down to using an aerial to avoid a grab; instinctive rolls, spotdodges, and shields will be caught. Pushing her opponent into the corner using her mobility is something that ZSS excels at, and getting grabs in that situation (or punishing an opponent for committing to an aerial to beat her grab) is not difficult.
Tether grabs are generally bad because the risk:reward ratio for trying to grab is bad. Hit, and you gain positional advantage. Miss, and you eat an f-smash or f-air. But ZSS' reward off a grab is good because of her aerial mobility: her pummel isn't slow, her throw damage is decent (7% d-throw I believe), and she can follow up with up-airs (7-8%) and up-b (KOs). So the risk:reward ratio is not so bad for her: her opponent stands to lose as much by shielding against her at midrange as she has to by throwing out her grab.
Overall, her grab is comparable to Diddy's recovery: it's a weakness in the sense that it's an average move on a character with above-average tools, and other characters with above-average tools can sometimes exploit that mediocrity, but even though it's an average move it does have some unique advantages (above-average reward and catching defensive options, in the case of ZSS' grab).
2) The obvious solution to short characters is good spacing so that ZSS can hit with jabs and n-airs (having a disjointed n-air that hits on both sides of ZSS' body and a jab that comes out on frame 1 makes it possible to contest small, fast characters), but an even better solution is perfect pivot, which helps ZSS with her long legs more than it helps most characters. Against Pikachu I like to use perfect pivot f-tilt. Angled up, this will catch Pikachu out of his f-air. Angled down, it will catch Pikachu out of his grab or up-tilt (blocking the tjolt too). D-tilt is slower than f-tilt but perfect pivot into d-tilt will hit Pikachu out of his own d-tilt. If I'm too close to Pikachu I will use perfect pivot jab. The perfect pivot here puts ZSS into optimal spacing to hit most short characters, though the timing is tight. I like to use perfect pivot up-tilt as an approach against short characters because of the way up-tilt starts up.
She received buffs from Brawl, but they aren't moveset improvements: they are engine/mechanics changes, and changes to other characters:
- Her recovery is much better now that her opponents can't just grab the ledge and send her to her death. Pikachu and Meta Knight could dominate ZSS offstage in Brawl, but that's no longer the case in Smash 4: between an unhoggable tether, a scarier up-b, and her flip kick, she's difficult to gimp or even edgeguard.
- Her air speed relative to the cast has become even better.
- Shielding is more of a commitment, so shields aren't as big of a deal against her any more.
She's one of the few characters who are good in disadvantage in this game: flip, b-reverses, landing up-airs, jump -> d-air, and her mobility get her out of bad situations about as well as Sheik's or Pikachu's tools. In advantage, she's also great due to combos like n-air to f-air and endless frame traps enabled by her airspeed.
In neutral, she needs to space well with up-airs and n-airs, time her d-smash and paralyzer pressure, and use all the options in her kit, including perfect pivoting, to stand up to other top-tier neutrals. To her credit, she's one of the better users of initial-dashing to weave in and out, an effective strategy that gains ground with each passing tournament.
I also think that she improves notably with customs. Whip Lash is good for stringing hits together. up-b 3 (the power version) packs more kill power and is more difficult to DI out of (but also more difficult to aim); generally, the better recovery from her other up-bs is not needed, because her tether and flip will get her back to the stage anyway, so I almost always pick this one. Shooting star flip kick provides her a safe way to land and, since down-b is not safe on shield anyway, is more reliable for what she actually wants to use down-b for: getting out of bad situations. Nothing is worth using over paralyzer, but 3 good options give her more than the likes of Diddy or Yoshi receive. Sonic (Hammer Spin Dash), Pikachu (Heavy Skull Bash), and arguably Sheik (Gravity Grenade) get more benefit than she does out of customs, though.
If I were to make a tier list, I would put the most consistent characters (that is, characters with the fewest bad matchups) at the top. It would look like this at the upper end:
Tier 1:
![Sheik :4sheik: :4sheik:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
![Pikachu :4pikachu: :4pikachu:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
these characters have no bad matchups, and are most consistent for tournaments. They have tools for every situation.
Tier 2:
![Diddy Kong :4diddy: :4diddy:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
![Zero Suit Zamus :4zss: :4zss:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
these characters have a few bad matchups, but have very dominant options against most of the cast. They may need to play around certain holes in their otherwise great toolkits (Diddy's recovery, ZSS' grab).
Tier 3: [3 or 4 characters here] these characters have multiple bad matchups or bad matchups with top tiers, but have strong options against most of the cast.
and so on. I'll refrain from making the entire thing because I don't want to start a discussion about why this character is here or that character is there.
I'll note that tier gaps in this inchoate list don't indicate a significant performance difference between characters. There have been arguments made in this topic that there should only be 3 tiers in this game because character differences "aren't that big." I disagree, because I think tier gaps should consist of whatever is most helpful in presenting useful information. Here, I would break tiers up by number of bad matchups rather than by performance gaps, which may be small in practice. In a series of tournaments, Diddys may place as well as or better than Sheiks at top level, simply because the Diddy may not run into his bad matchups or they may not be disadvantageous by enough of a margin for someone like Zero to care (or, perhaps, those bad matchups aren't being played by other Zero-level players).
The schema is: [0 bad matchups "is a tier better than" 3-4 bad matchups "is a tier better than" 5-6 bad matchups "is a tier better than"....]. There is some weighting for where these bad matchups land, too (having bad matchups against Top Tiers is bad, because players are more likely to pick those characters up), but not too much.