I'm more-or-less resigned to just racing things as much as possible and hoping for the best. Scythia is even more dirt poor than Germania, so there aren't that many big armies. My next plan is to try out an army of all or nearly all light cavalry, which comes quite a few turns earlier than Chosen Archer Warbands. The missile-heavy Scythians seem like an ideal foe to face with such an army. When I don't have to tech up to tier 3 before I can get a well-suited force to fight Scythia with, I might be able to beat Egypt to victory conditions.

Basically, I'll sweep up field armies with my light cav, and bring a heavy assault brigade along to take down settlements. Luckily, Scythians are barbarians, so no heavy assault lifting is going to be needed to deal with their city walls. Simple axemen should be plenty to do the job.