It's only Second Coil that was severely nerfed (sans T9) because people back when complained that it was too hard (T7 was a wall for people
because things like this could happen). The nerfs in Final Coil only applied to the trash mobs outside of the boss arenas.
All of that said, one (or more) specific mechanic of Coil fights can make or break a random DF group. T7 could have Melusine hitting like a truck (with instant kill Flaming Circles) because people didn't pay attention to their Cursed Voice/Shrieks. T8 could cause wipes because no one was handling the towers, OT didn't stand in the boss to prevent it from turning when it confuses the MT, no one stacked the right amount for Ballistic Missile (if you've run ARF, you'll notice that most DF randos never stack right and always run away with/from Gaseous Bomb), or Allagan Field in general.