Mind if I join in the fun?
Cretian metallurgy may not get anywhere, but simple examination of the strange blood-metal from across the sea will reveal that direct sunlight causes metal to heat up, possibly to the point where it burns at a touch. This leads to the development of the
heat metal spell, a powerful military advance against the Jongans.
Knowing the importance of food, and incensed by the destruction of their own farms by fire, I suspect that the Cresian priests would pray that the same indignities be inflicted upon the enemy; if the Jongans show so little respect for the Field-Father, then let their own lands go barren!
Diminish plants would have a marked effect on Jongan agriculture. Of course, this requires that druids actually sneak over to the Jongan islands, and they can ill afford to lose any more members of their priestly caste. But the spells are subtle and require no direct contact with the Jongans. By the time the Jongans realize what’s happening, it may be too late.
Once the Cretian shapeshifters master their changes, they too can participate in guerilla warfare in Jonga, becoming truly fearsome spies and assassins. While advanced espionage lies far in the future, poisoning a well or a granary would be child’s play for a shapeshifter.
Do the Jongan wizards use spellbooks? I gather that the Cretians may not even have writing, in which case books will appear to them as some kind of bizarre magical talisman or fetish; but once they understand how important spellbooks are to the Jongan wizards, things can get nasty. All it takes is one hungry rat, bookworm, or other vermin to sneak into a wizard’s home and ruin his or her spellbook…
The Jongans, for their part, seem more culturally sophisticated than the Cretians, and are more likely to come up with high-level military tactics. Their bards will undoubtedly develop
whispering wind, allowing the Jongan units to co-ordinate over long distances and making it easier to track down Cretian agents on the islands. Likewise, their wizards can use higher-level versions of
flare as a signaling mechanism, thus passing along basic information to all other units over a wide area.
Ultimately, I don’t see a final winner in this conflict. This is a war of retaliation, not of conquest, and the battles will only serve to deplete each society’s manpower and resources. The Jongans, with their superior weapons and tactics, will win most pitched battles, but Cretian guerilla tactics will gnaw away at their infrastructure. Eventually, both sides should be sufficiently exhausted to dictate a
de facto truce.
If neither culture crushes the other immediately, the Cretians have the advantage in the intermediate term, as their druids can guarantee a perpetual surplus of food, something the Jongans cannot expect. However, they seem to have a relatively complacent, hide-bound mindset by comparison to the Jongans. However, if the Cretians don’t take advantage of their faster growth to conquer or crush their opponents, then Jongan technological savvy and magical ingenuity will give them a long-term advantage.