Reavers are anti-infantry specialists. Berserk only works if they kill their target. Throwing them against a Khador Destroyer (ARM 20) is suicide. They will bounce off, do no damage, and die for no gain.
In competitive play, Rhydon and especially Rhyperior are valued for their incredible strength and endurance. A "crusade" could metaphorically refer to a player's strategic effort to dominate with a specific set of Pokémon or a particular team composition. rhyas crusade the aradias reavers link