What annoys me most about the crafting feature is the randomness of the mythical object. The whole game draws its fascination (atleast for me) from being based on careful planning, buildup and optimization.
There are some random elements in fighting (enemy setup, terrains, and damage numbers), but a single win or lose does not change the overall costs of a city expansion or a tournaments much; plus the randomness can be countered to a certain extend with effort: careful selection of own troops and manual fighting. It is my own decision if I am too lazy to fight manually or at least check the terrain in advance.
The third Grand prize of major events is sort of random - you do not know exactly how many double days you must take to get it, but can calculate it roughly, and if you fail, you do know that it was your own fault, because you could have been less risky and less greedy on single days.
Daily prizes of events are also random, and I usually end up getting 50% more daily prizes on my most successful town versus my least. This already causes a lot of bickering among players, but I can live with a difference of 8 versus 12 in spring/autumn or 10 versus 15 in summer/winter.
Now you are introducing a new "exciting" feature, and after a whole week of stitching minor things together, you open op a mythical bubble and either celebrate a new Venars Rock, or wreck your keyboard because you already have enough time instants. This is a 0 versus 1 situation, much worse than daily prizes. And this is supposed to be the Grand prize of crafting. Remember: "crafting", not "gambling". If you complete the effort and do everything you can, but then fail on one single final die roll, that feels like the game shows you the middle finger. This does NOT fit with an optimization game.
So my request would be: Get rid of that randomness or at least reduce it to reasonable levels.
A reasonable level would be like: Make "Grand prize" recipes, which cost swirly mist (or whatever that currency is called) instead of producing it, and those recipes create Venars Rock or whatever greater prizes you are willing to give out. At most one grand recipe active after any reroll. So whether you get Venars Rock would still be based on randomness (the recipe may or may not appear for a while), but at least you do not lose all your stuff trying to get it.