can someone explain to me why isn't lucario banned from using copycat?
if your opponent does not have a pokemon faster than lucario then lucario can keep spaming copy-cat and use roar to deal cheap damage with entry hazards.
why isn't this anti-competitive strategy banned?
I know that in gen 5 assist was banned for this reason.
Assist Ban is one that I don't agree with at all, but there are differences here:
1. Lucario requires to use Hazards + a Ghost himself in the team to work. Assist required Ditto and opponent to use Hazards.
2. Most important thing, Lucario requires the opponent to use Roar or WW and Lucario to appear. All teams use Hazards, but not a high percentage ( I would say like 30% at most) use Roar or Whirlwind. Not only they have to have the move, they also have to click it on the specific battle Lucario is in, after Lucario's team has put enough Hazards and Lucario specifically has to be dragged in to work. Very unlikely scenario.
3. Assist was much more difficult to stop once the cycle started. Lucario can be stopped by:
A. Faster scarfer.
B. Priority.
C. Protect/Endure.
D. The rare but viable Cradily. I won't count Soundproof, Magic Coat and Octillery, but they also work.
E. Hail. Lucario is damaged by it, so he will die in 16 turns at most. Probably earlier, since Abomasnow and Walrein run Protect often.
Hopefully this helps.