I mean, this was predictable to happen. There is no Ferro to trap, Skarmory is terrible (but even then good enough to hit Zone hard with Body Prese) and the other Steels have ways to circunvent Zone.
So, the "solution" for Zone is to make use of what it accomplishes, mainly forcing opponents to Tera before they would like:
Step 1: Put Balloon on Zone. This allows to switch into Treads and damage it hard.
Step 2: Use Mons walled by Steels but with enough power to break them if they are already damaged. For example, choiced Enamorus struggles vs Treads and especially Corv, so if Zone doesnt kill them but damages them, thats a win. Similarly, if your Enamorus doesnt switch out vs Scizor, but continues to use Moonblast, Scizor either is worn down or trapped by Zone after killing Enamorus. In the second scenario you should obviously have something fast to not be vulnerable after Enamorus dies.
Step 3: Use Mons almost fully walled by Tinkaton and Gambit, or annoyed by them. Tinkaton is an early game Mon that puts Rocks and annoys stuff with TW, Encore and Knock Off. So, the moment Tink appears, you send Zone. Zone doesnt care about TW and Knock, so you just have to have counterplay to whatever will set-up after Zone dies. If Tink Teras, thats a win for Zone, Tink is a bad Tera user overall. Meanwhile, Gambit is a very good Tera user, but not early game. So, if you attract Gambit early game ( offensive Blastless Gholdengo or Pecharunt do the job) and trap it with Zone, you likely lose Zone, but Gambit will be either very damaged or already Tera'd, meaning it wont surprise you with unexpected Tera type in late game. Thats also a win for Gambit team.
So, with that in mind, a good Zone team would be something like this (just thinking from ny head, not actually building) :
1. Zone (lmao, what a surprise).
2. Enamorus (attracts Treads, Tink and Corv)
3. Pecharunt (pivot and attracts Gambit)
4. Tusk, Lando or something similar (again, attracts some Corvs and somewhat deals with Gholdengo and late game Gambit).
5. Clef or Tinkaton (Rockers that despise Steels).
6. Fast Mon thar covers stuff. Many options here, Pult, Weavile, Waterpon, even Gambit kinda counts.
So, the goal of Zone is not to actually kill stuff (except Tinkaton and the suboptimal Pdef Corv), but to force the opponent to change game plan, preferably an early Tera.
Of course, there is always the Specs Analytic Zone, but that is an entirely different threat that plays very differently and with different teammates.