>>42527701Make things difficult but fair. The player shouldn't be able to win battles with any team but they player should be able to win battles with most teams.
More important than just making trainers difficult is giving the player access to strategies, like weather support, tailwind, trick room, or other options like that.
Having said that, the vast majority of players will catch two Pokemon on Route 1, give every mon four attacks without trying to think of a strategy beyond attacking things until they die, and will then blame you when they lose because the game is unfair. You're just going to have to accept that being the average Pokemon consumer and the majority of your game's potential playerbase.