I do agree with you, when say that the approach is not right if we want to have a exact BIS equipment.

Model is non-linear. If it was, scale factor would always be the same and model would be

DPS(haste,crit,sp,hit,int,sp)=Fixed_DPS+SF_haste*haste+SF_crit*crit+SF_SP+.....

But we saw that SF change depending the gear you have. So SF_haste would be a function like SF_haste(haste,crit,SP,...).

Scale factors are fined for a one by one equipment switch but not to find a combinaison of gears.

However, I think that simcraft has done most of the reverse engineering to get a model close enough to the wow reality.

Is there any mathematical representation of that model ?

So why not just trying every combination but use the simcraft result instead of using scale factors ?

For the programme, maybe could you how us a sorted list of the best in slot gearset instead of the very best that nobody won't ever see ^^.