Single player pokemon has 3 basic team building strategies....
- Stall Core: Using a core of 2 or 3 defensive pokemon to shutdown your opponents offense, and set up the field with weather, hazards, etc to make it favourable for your own offensive pokes
- Hyper Offense: Use a fast suicide lead to quickly set up hazards, weather, etc OR deal heavy damage, then use your free switch to send a pokemon with a type advantage to your OP, plus the power to 2HKO virtually any pokemon in the game
- Baton Pass: Use stat buffs, status, field/weather to create a super pokemon that can't be taken down easily
The problem with many unofficial communities(like Smogon) is that they've taken the stance that strategy 1 is the "correct" way to play, and that the other strategies are gimmicks.
So whenever pokemon/abilities crop up that shift the balance of the meta away from Stall, they get banned.
The actual balance issues with single player are a bit overblown. But players don't want to change up their strategies or think a bit outside the box.