The Goblins finally started clicking for me when I realized that population isn’t something you’re supposed to maintain carefully: it’s a resource to be spent. Spend population to smash crystals, to attack people, etc. And it’s a resource that limits your movement. (Also, Ferocity is likewise a resource to be spent–you’ll get Ferocity back pretty readily, unless your opponents are playing passively, which is good for you anyway.)