Fairy is ALWAYS going to have to sack at least one Pokemon to stop Scizor, that's pretty much guaranteed.
If Rocks are up at all, Scizor is going to decimate a Fairy Team if it gets off a SINGLE Swords Dance. Steel has plenty of viable Rock Setters, that's not an issue.
+2 252 Atk Technician Mega Scizor Bullet Punch vs. 252 HP / 252+ Def Togekiss: 324-384 (86.6 - 102.6%) -- guaranteed OHKO after Stealth Rock
That's a 100% Defensive Togekiss.
+1 0 SpA Togekiss Hidden Power Fire vs. 252 HP / 0 SpD Mega Scizor: 304-360 (88.3 - 104.6%) -- 31.3% chance to OHKO (Download would be the only offensive option here)
If that Togekiss isn't 100% Defensive, Scizor walks all over it after SD is up. It relies on Paralysis proccing to win, as it can't abuse Paraflinch even with Serene Grace, it's all on Paralysis, as Scizor would always move before Togekiss unless it uses ExtremeSpeed for some reason.
0 SpA Clefable Hidden Power Fire vs. 252 HP / 0 SpD Mega Scizor: 168-200 (48.8 - 58.1%) -- 98% chance to 2HKO
252 Atk Technician Mega Scizor Bullet Punch vs. 252 HP / 252+ Def Unaware Clefable: 192-228 (48.7 - 57.8%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
Mega Scizor also walks all over Clefable. The same goes with all other Scizor variants, it's either a 2HKO, or Scizor can set up SD and make itself even scarier on the first turn. Even Modest Clefable can't 1HKO a normal Scizor, and if it goes for 252 HP/Special Attack, it's getting 1HKOed, or has a 30% or more chance of being 1HKOed by anything but an unboosted, non-Choice Band normal Scizor.