So here's the thing:
If you were to train your pokemon the regular way, you would kill hundreds, if not thousands of pokemon you find in bushes
You know none of them pose a threat to the pokemon you're training, and you always have a healing center at hand

So tell me. Why would you spend possibly several weeks to do this, instead of just duping rare candies and be done within an hour or so?
How is your life improved, having mindlessly grinded your pokemon to max, never facing a challenge while doing it?
You just wasted weeks of your life, while someone reached that goal within the day, and got to continue playing the game, and you didn' even enjoy the grind, just had to do it.
If a grind is incredibly monotonous and requires constant repetition of something that takes minimal input from the player and poses no challenge, then you should always cheat in whatever it is that you're aiming for, otherwise you're just wasting your time.

HOWEVER, in the case of Pokemon games, don't fucking grind or cheat, you don't have to, the games are piss easy, the trainer fights give you more than enough XP to progress and you only need to understand the rock, paper, scissors gameplay, levels won't matter all that much unless there's a massive gap. And don't hoard consumables, use them constantly, especially stat boosts.