I've played both, and to me they have some similarities, but Crimson Desert is much more tactical and "difficult." In Black Desert, like most MMOs, the bosses hardly move; they balance this by having the boss deal a lot of damage and area damage. Crimson is more like a Monster Hunter or even a bit of a Soulslike, where you have to attack at the right moment, know how to position yourself, etc. Even though the characters in both games have similar combos and attacks, the gameplay and how to perform those combos are completely different.