About the pickaxe, well, you might have a point there. But, maybe there's also a lot of wasted material, because this is your first attempt at making the tool? Also, it's a huge pickaxe. And, finally, it's a mythical world = so some things probably would not be very logical. But seriously, yes, it's kinda skewed = the price to enter the bronze age is very steep. But then to enter the iron age, the price is steep, too, as you are asked to go into a very dangerous biome. Then the price to enter the silver age is 'high' because of the wolves and such, who guard it. So, theoretically, there is some sort of balance. Although to me personally, the bronze age was a lot more grind than the subsequent metals.