It's not just the bone widow, it seems to me like all summons except for the incarnate itself haven't been balanced well when the player has mostly points in summoning. My only explaination is that the devs overlooked how the artillery plant and bone widow summons scale in that case.
Look at this example. Here I attack a party member. The top is the artillery summons ranged attack, buttom the incarnates ranged attack after farsight infusion. Granted, the artillery plant ranged attack has a two turn cooldown, the Incarnates ranged attack only one and also costs one AP less. But still, this kind of damage just feels like a glitch.
I don't believe that one source point is supposed to be the difference between a dent in magic armor and an almost instant kill.
The devs must have playtested the bone widow and artillery plant with a character skilled in necromancy/geomancer and none in summoning. This would also explain the hugely inflated HP values of the bone widow.
That the Incarnate does so much less damage despite the summoner being designed mostly around him doesn't seem right.