Given that Tristain always had shittons of mages for it's population, and that they then gained 60,000 more mages, I would say that quantity of their troops that use magic of some form is one area tristain will probably always have the advantage.
Not to mention the gold Fae brought with them. So why not pay for aditional mages and mercenary troops from Germania, Romalia or even Galia?
Sane