Exploits should involve something that the dev clearly overlooked when they wrote the code.
For example, the "retreat" mechanic never track who retreated so you can rejoin the fight for infinite turns as long as it's not over yet without giving enemies future turn, making any hard fight ridiculous easy because the enemies will never get to act more than once.
That is an example of exploit and can be fixed with 1 or 2 simple line of code to prevent giving people who leave the fight and reenter in the same turn another round of action.
This, however, is just preparing the field and making creative use of skill, something that Larian clearly support with their trailer on how you can just teleport people into instant death pit or that crazy balista insta killing enemies.
Can we stop everything that is useful and smart as exploit? I'm doing the fire mage boss and if someone calls me stacking 100% flame resist an exploit, they should stay away from turn-based game.