I fell like they could've added a lot of fun activities on the island or something and you'd get crystals depending on how well you did.

Like one of them could've have you defending a settlement. In between attacks, crafters and gatherers could build things in order to buff the settlement defenses. The attacks would be easier or harder depending on how well you built it up. The rewards would be dependent on how well you did the attack.

You know, activities that spice the gameplay up. Literally anything other than grinding mobs in a zerg rush.