Thank you for your in depth analysis.
I can just say you are right, the problem is our "algorithm" scales with diffuculty in 2 or 3 direction at once, which is absolutely not a good idea (was written in last day if I recall correctly, if we are going to do something more about it I will take your calculations into account). How our system works is: Depending on your level(difficulty) +- some random you get a time, and then every output item has some point value(3 hard items has them hardcoded, and then a random semi could spawn which has point value for the whole group), we then subtract from the difficulty by these item points till its 0(I can only agree the time should have been calculated at this step). The score you get for completed item is based also on your difficulty(so in higher levels you get more points) the item lookup point value and also the time it took you from start.
If I remember correctly I wanted to do something as you describe by going through all the recipe lists and calculating time it would took, but similiarly as with Customizer Machine or In Game Recipe book, there just wasnt enough time.
Thank you for feedback and have a nice day.