Yeah, the "realistic" option for fiery Androphag arrows would be for the poison to be consumed in the flames. In other words, flaming arrows would replace poison arrows, not add to them.
Then again, it seems a bit silly to mention "realism" when discussing a game that already includes flesh-eating giants, demon monkeys, Squid from Beyond the Stars, and Tartarians.
As it is, I think that the current situation sounds fine to me. It's not like Sauromatia is lacking archers! They can just recruit a bunch of guys with composite bows at the nearest fortress....