There is some rng atm but you can avoid it by finding all the mats in the game. For example, today i wanted to put a 8% spell damage increase on my neck. The cheapest way to get it was:
This has the spell damage proc and 3 others i dont want. Those mats are very easy to find too. But ended up doing:
These mats are a bit more time consuming to find but will give me the spell damage proc 100% of the time. I like how it works now and think you need to keep it like this in order to make a large variety of mats relevant.
An idea to the devs to make it even more complex- have some stats cancel out their opposite- for example have +2 order would also do -2 chaos, +3 Life would do -3 Death. EDIT on second thought it might be easier for balance just to have negative stats put in on an item by item basis rather than an across the board rule that opposites give negative stats.