I agree with Jimera0 about Terrakion needing a suspect round.
The list of Pokemon that can actually switch-in on CB Terrakion without getting 2HKOed are:
Cofagrigus
Cresselia
Dusclops
Gligar
Golurk
Nidoqueen
Qwilfish (Intimidate)
Shelgon
Tangela
Remove Nidoqueen & Qwilfish if Terrakion has Earthquake
Gligar can only hit it with a EQ from a feeble 186 Attack. Shelgon can only Phaze with Roar or Dragon Tail. Cofagrigus, Dusclops, & Tangela can only hope and pray that Will-O-Wisp or Sleep Powder hits.
Cresselia and Golurk are the only true
counters to it, using the term "counter" very lightly here as they both take upward of 70% from 2 Stone Edges, leaving no room for error.
And then there's Hazards and Sand damage...
Once Keldeo gets released, I know that either Terrakion or Keldeo is getting the boot as there's absolutely no way any team can handle Band Terrakion & Specs Keldeo at the same time. The metagame would just implode at that point.
You can argue DW OU is okay with both, but DW OU has Excadrill, Garchomp, and Shadow Tag Chandelure making Choice-locked Rock and Fighting moves absolutely TERRIBLE in the tier so DW OU doesn't have the same problem OU has with Terrakion. But I suppose what happens with Keldeo still remains to be seen.
And that's without getting into the can of worms that is the fact Terrakion can run any set it damn-well feels like. SubSD with Rock Gem pretty much dismantles any common Terrakion switch-ins, even dealing with Gliscor with ease should it get a Sub up on the switch.
terrakion is not broken at all, each set has counters and while it may be "over centralizing" that doesn't make it bad for the metagame, it's used less than scizor no body ever claims that to be "over centralizing". Being used allot does not warrant a ban neither does being unpredictable. It does have nice synergy with volt-turn but so do most threats, terrakion is not the only pokemon that needs one turn of setup to destroy teams there is dragonite, salamence, cloyster, CM latios, haxorus and more yet none of those are being called broken. I think the issue with terrakion is that it came out of nowhere to be a top threat and while it has been around for a while new sets are appearing everywhere like the rock gem set or sub swords dance, if time is given for all viable terrakion sets to be thought up and used, then terrakion will seem like much less of an issue
Well Scizor is beaten by damn near every Fire-type in the game not weak to Superpower (It's an exaggeration, I know, but you get the point,) Steels like Skarmory, Bulky Ghost- or Water-types, and the dozens of Pokemon like Celebi & Rotom-W that commonly carry HP Fire.
Terrakion, on the other hand, is beaten by absolute fuck-all, the most extreme degree of nothing. Anything that CB Terrakion can't 2HKO (All
nine of them) get absolutely blasted by SubSD + Rock Gem.
It almost entirely breaks the system of checks and counters as nothing can switch into Terrakion twice. If a faster Pokemon isn't OHKOed by CB Terrakion, it is 2HKOed, meaning it can't switch-in twice. If a slower Pokemon is only 3HKOed, Terrakion attacks it on the switch, switches back out, comes back in and KOes it
guaranteed the next time it comes in as it can't take 2 more attacks.
The difference between Dragonite, Haxorus, or Salamence and Terrakion is that Terrakion doesn't lock itself into it's STAB move for 2-3 turns. You can't revenge Terrakion without Dugtrio. He can just switch right out. But the only way too beat Terrakion is to revenge him. Do you see that massive flaw?
The difference between Cloyster or Latias and Terrakion is that Terrakion is not only naturally fast, he's naturally powerful with near perfect coverage in his STAB attacks alone. Besides, Latias has a Base 90 STAB and Base 70 Coverage move? Oh that's cute. Terrakion has a Base 120 STAB and a Base 100 STAB for coverage.
None of the Pokemon you're comparing Terrakion to can actually be compared to Terrakion.
You're severely underestimating the community when you say that we haven't adjusted to Terrakion. We know exactly what we're dealing with and unless we all start using Cresselia or Nidoqueen, we've adjusted as far as we can.
Terrakion needs to go.