It comes down to the design philosophy of the game.
Townsfolk are the most common, and so they have the most variation in how useful they can be. Compare how involved Alchemist feels compared to Chef.
Outsiders are more or less a second thought for the Storytellers, unfortunately, since they mostly just have effects rather than helping to solve the game like Puzzlemaster.
Minions are limited in number and their abilities need to counterbalance the good team enough to be worth getting rid of, rather than being as forgettable as evil Outsiders.
The Demon is stressful and all-impactful, even though most of their secondary abilities are kinda moderate.