I think that due to the difference in the experience point multiplier between pets and characters, pets level up faster than characters. I'm sadly letting them die to lose experience points and prevent them from exceeding my character's level, but it's so frustrating. I would be happy if there was a way to prevent pets from exceeding the character's level, or if it were possible to control pets even if they are higher level than the character.
Sorry if this is difficult to understand, as I used a translation machine.