Okay. 8 moveslots on Mewtwo, Arceus, Kyogre... Guess how stoppable they'll be. I'll give you a hint: They won't be. --- I'm not easily impressed; I'm usually oblivious to whatever's in front of me. Stunfisk is the epitome of monstrous majestic legendary creatures that spew fire.
The anime doesn't have to worry about battle mechanics and the writers control what can happen. In game, it's unlikely that a fully trained Pidgeot or Raticate would beat something like a Garchomp or Hydreigon, but in the anime they'd be on equil footing, like how Pikachu beat an Onyx or a Rhydon.
Also, if they didn't limit the number of moves, you'd run into really annoying battles where you'd have to fight a Smeargle with every status effect, every stat increase/decrease, and attacks of every type. --- PSN: Zekryn 3DS: 0318-7077-9952