system
Given the following post, respond as if you're commenting on Reddit:
human
[Pokemon Games] What stops someone from buying 100 rare candies and beating the Champion and rule the world?

I'm basically asking what is stopping someone from carefully selecting a team and leveling it? Are the game mechanics and items just there for the players convenience or you really can teach Pokemon from CDs? And while we are at it why are Gyms usually specializing in type rather than stuff like speed and defense?
gpt
Rare candy's increase the level,  but do not increase the bond with your Pokémon, nor does it give them the time and real experience to use their skills to their fullest, nor the trainer the same experience.

Gyms running by type is more a community aspect than a function. They gather people of like mind, and temperament that understand the abilities and care of the type of Pokémon and truly love them. If they were based on speed, or defense then people would focus on only the "best" or "most powerful" Pokémon instead of the companions they love.