With these guides you do not need to level up KOTR or master Mime twice (which takes forever), and you don't need to spend any time leveling up your party beforehand, which I've found can get very tedious as well.
By attaching the double and triple growth weapons to your characters, you can get an enourmous amount of AP for your materia, which is a huge benefit. So why waste those valuable materia slots on mastered KOTR or Mimes? This is the only chance of the game to gain this much AP, so you may as well take advantage of it. I hope this can be of help to you, defeating both weapons is the most difficult challenge of the game. Good luck.