Er, I was never contesting the fact that for high armor AI is better.
Also, the 90% damage from AI seems to fail sometimes, and does 100% damage, probably would apply to DS as well. Dunno.
I should say I base my facts on the actual calculation and is assuming this is a PvP situation. (where AI has a cap of 35)
It can be proven by simple math...
According to the calculator (using hatchet as an example coz it has both AI and DS)
125 str 100 anatomy tactics and 100 DI
Hachet has dmg range of 47-54 the average of this is 50.5 after 70 resist is an average of 15dmg per hit...
Even if we ignore the 10% dmg penalty from DS both hits land it's still only 30dmg, in order to achieve 35dmg in a DS with a hatchet you need average dmg of 58.3 per swing which is impossible to achieve without spending skill in Lumberjack. (150str 120 anat tactics 100DI gives 51-59 avg is only 55).
Now in order to achieve 35dmg AI everytime you need min dmg at at least 39 (which is achieviable at only 100 str 100 tactics ZERO anatomy and 100 DI you dont even need that human 20 anatomy).
Equal skill AI's 35 dmg will happen 50% of the time, while DS will happen 25% of the time.
PvP ONLY: Again DS gives nice burst (with possible double procs on hit spells), but you need heavier weapon to go with it, and DS isnt reliable unless your opponent is disarmed (otherwise you will be wasting a lot of mana at the whiffing).
In PvM: If whatever you are trying to hit has at least 50 resist in it's lowest resist, AI beats the crap out of double shot, and you really dont want to put instant hit spell on DS weapon because lighting procs will ignore all the Perfection, EoO and Slayer bonus dmg you should get. ALSO if the mobs you are trying to hit has low resist but high wrestling skill, but you dont have a discoder with you (you are whiffing a good amount) AI will still be better.
DS can be better than AI but it's simply ultra situational. AI will work on anything and everything and get identical outcome and the only time you will lose dmg using AI is when the monster has a resist (that you are attacking against) lower than 10.