[Belac]

Everyone else is under the same constraints, so one must accept that research gets a bit slower once you've researched good battle magic.

Also, most nations are such that their weaker mages are more cost-efficient researchers. So once you have multiple forts, recruit cheap mages from most of them and battle mages from a few. Use the money saved by not recruiting lots of super-expensive mages to put up more forts, and eventually your research catches up.