Right now tempering feels bad. Making it RNG based I don’t think is healthy long term for the game. I think there are probably various things Blizzard could do to improve it, but one thing I thought of is this:
Every time you masterwork, the potential “crit” changes in a sequential order and this is actually visible to the player. So, when you first masterwork an item a single time, one of the stats maybe will glow. What this is showing is that this specific stat would crit IF the next masterwork were to be a crit (4,8,or 12). What this allows is for a slight minigame feel where you are masterworking several things at the same time and “gaming” the system to crit exactly what you want on a specific piece of gear.
So for example, lets say you want to crit “vulnerable” on a ring, but the vulnerable stat is the 4th stat on that ring. The current “highlighted” stat is whatever the 3rd stat is and you are doing your 3rd masterwork. You masterwork and now the next stat that is highlighted is the 4th stat and in this case, you happen to have a vulnerable on this specific ring that you want to get crit. If you masterwork again, WHATEVER item you masterwork next the 4th stat on that item will get crit (since its sequential) so you masterwork the ring you wanted and the vulnerable on that ring gets the crit. You can keep doing this for all different items. Maybe you purposefully crit on trash items because you dont have a good rotation but this allows you to game the system to get crits on items you want instead of it being random.
Note: I think a similar sequential system would be really nice for rerolling stats as well, where you are constantly going through the next 3 available stats an item can roll so that you will always have the opportunity to see the stat you want relatively soon instead of rolling into the millions of gold…
2nd note: The same concept could be applied to tempering where every time you reroll a temper, it goes to the next stat in the manual for that item so that you aren’t constantly rerolling the same state over and over.
Remove the RNG from these systems and make it engaging.