Your math on the last example is confusing me . . . what are you calculating in that formula? Why is 0.65 on the denominator?
35% Quicker =/= 35% More Items
The way the artifact works is that it reduces the time required to craft. This is inverse relationship as crafting rate is item/time. So, when you reduce the time, you reduce the denominator. Thus, to find the increase it is 1/(1-0.35)=1.5384 or a 53.84% increase.
This is easily demonstrated with the AP boost of 50%. A 50% boost results in doubling your crafting speed, or a 100% increase.
Additionally, Crafting speed increases are multiplicative with one another, not additive. So.... a 50% AP boost and a 35% Epic Crafter Speed results in 1/((1-0.5)*(1-0.35))=3.077 or a 207% increase over base.
Basically, all the Increase Crafting Speed artifacts are stronger than they appear: (1/(1-x)-1)
Poor=5% = 5.3% increase
Common = 10% = 11.1% increase
Uncommon = 15% = 17.6% increase
Rare = 25% = 33.3% increase
Epic = 35% = 53.8% increase
Legendary = 50% = 100% increase
Insane = 65% = 185.7% increase
Max crafting speed is 50% AP + 3x10% Techs + 65% Insane Artifact
1/((1-0.5)*(1-0.1)^3*(1-0.65))=7.838 or a 683.8% increase