Been wondering this for awhile but there are two things that the Ascians seemed to have thought of let alone try over the thousands of years. One is time travel as the idea didn't seem to have come across their thoughts. Course we don't know when they first came across a shard of Legorith as the only one we know of is the only one that seems to have an affinity for time based magic.

The other thing at least according to Emet when choosing to allow us to go on a Lightwarden killing spree is the idea of trying the diplomatic approach. You'd think they could have tried with the Allagans or Mach.