You shouldn't expect an easy time in a biome you are not prepared for, e.g. you haven't even "finished" the previous one. That makes sense. I did feel like difficulty didn't ramp up evenly. Transitioning to plains felt like a bigger jump in difficulty than transitioning to other biomes. On the other hand, that's currently end-game content. Maybe difficulty will be smoothed out as more biomes are added. Once all content is there, it makes sense that there could be more rebalancing so it all fits better together.