In the early days, mages were less powerful because there was less power in the Aether. Their most powerful spells could only destroy small houses. Plenty of small houses were destroyed as these mages learned their skills, but it was mostly their own houses, and they learned from their mistakes. Over time, these mages not only became more skilled at their craft, they also improved the power all mages had to draw on, weaving isolated pockets of Aether together into one large Aether-net.
Through this, the mages were able to accomplish much, much more. But it meant that new mages could draw on power far greater than a new mage knows how to control.