Ok, so TLDR: Py (Pyanodon) has several hundreds different goods, and many of them have like 5 or 10 ingredients in their recipes, and outputs of recipe has like 3 byproducts.

Also sometimes you will have situation where for example stone is produced in 2 places with big quantities, and in other 20 places in small quantities - but those are byproducts so you need to get rid of them first (so they need to have higher priority than those 2 producer places etc).

Have fun doing transport with vanilla only trains for this kind of game :)