Ok so if you think about it Lucario haven´t been used nowas there is more powerful Attackers like Conkeldurr, Breloom or Bisharp as an example. The main thing was that Lucario got a powerful mega with amazingly Attack Stats and was used too much very much right now! And when they banned it to Uber Lucario wasn´t used as much as before. The same is that it got many other Pokemon in OU that outclasses it like Mach Punch Conceldurr or Sucker Punch Bisharp that gives more power.
