This is a bug or an unclear and really underwhelming passive and I would like to have the answer ^^
So “Mass production” passive says : “Chance to forge weapon increased by +32%”
With the “+” I understand it as an additive chance so 20+32=52% chance to summon a weapon.
I tested it on a dummy, for 50 Forge Strike, I summoned 13 weapons --> 13/50 = 26% chance
So with this result, I see that the +32% increased chance is actually just an increased not an added chance ( 20*1.32 = 26.4% chance).
In this case, putting 4 points to have 26% instead of 20% chance to forge a weapon is really bad.
So, if it was suppoed to be added chance then it is a bug, if it is purposely an increased chance then it should not need 4 points in it.
Hope I will have your answer soon , bye !