Supposed to be temporary?
Definitely not. At a minimum, it’s a playground to try new things. And for games lacking a deep/replayable endgame they can be used to add depth or new types to choose from.
The POE/Torchlight Infinite/Last Epoch model is not what the bean counters want. They want to save big permanent additions for paid expansions. Even though they’ll make a LOT more money, and retain more players, if they add substantial content each season. Players that will many times buy the battle passes if they really enjoy the game.
The minute they realize their design is flawed is the minute they can really improve the game with each season.
Class balance will remain a mess as long as they keep adding borrowed powers each season as well. As certain builds benefit much more than others each time.