RNG would be like card counting in a casino while using an AR is like mind-controlling the dealer to give you whatever cards you desire.
As you can see, RNG works because you UNDERSTAND how the mechanics behind it. It takes skill, time and effort to pull it off. And even then, it's not 100% foolproof. Just like card counting.
Meanwhile, with an AR, you press A to activate. And it works. Every. Single. Time.
You just described selective breeding vs RNG, not RNG vs AR.
With RNG, you're also manipulating the game. The game is meant to be completely random. RNG is exploiting a fault in the randomness of the game to get what you want.
I personally don't take the time to learn RNG because 1) I don't have a DS Lite, with which it's much easier to do the process, 2) Pokégen gives me a legal, perfect Pokémon ready to be used in competitive play with much less effort and without the possible side effects of using an AR on your game (which are urban legend anyway but let's not get into that).
Amount of effort isn't a factor in defining what's a cheat. RNG definitely takes much less time than using the mechanics the game makers actually intended us to (selective breeding). It may be near impossible to get a perfect Pokémon with selective breeding, even though a perfect Pokémon is not always needed.
Also, many RNG breeders use gen'd Dittos to begin the breeding process and think it's perfectly fine and not cheating.
I'm not against it (the various methods), because I can very well use them myself, and it levels the field when even the PWT Pokémon have perfect IVs which regular players would otherwise find impossible to get, and you also don't win instantly by having an assortment of perfect RNG'd or gen'd Pokémon, but it sure does break the game and means Pokémon is a completely flawed game, because all the mechanics of the game are pointless when you can just generate a perfect Pokémon from scratch, or manipulate the game so that it generates one for you.