If the player has control of the Drapanai and puts a few units in front spread into loose formation to absorb the bulk of the initial volleys, then hopefully the other Drap units behind would not be so depleted and this could allow them to close with the Toxotai without being annihilated. Once melee ensues, the Drapanai will certainly win. Now if the player has control of the Toxotai and manages them well, avoiding melee, the Toxotai could certainly win as well.
As for routing, I don't think the Draps would rout due to missile fire. They have too high morale for that (especially if the units they are going to engage in melee are only Toxotai). It's more likely that they'll simply be shot down to the last man.
I think it's really decided by which side has a player controlling and which side the AI. But I voted for Drapanai just to even up the poll.
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