Legend items: when rerolling the values of affixes, they wont go below 75% of their maximum value as long as the item is a Legend Item (read this in an old post). non Legend items, when you reroll their values, can end up giving you numbers anywhere from the minimum value to the max, so it is harder to get max values with these items. if the item is Legend when you add a Mythic affix, it is still considered a Legend item, or more properly, a Mythic Legend item. your Chakram is basically a Mythic Epic item, even if you put some Legend affixes on it. even with +25% Item Quality, it might take more crystals than usual to get the values maxed out. I find that if I have at least 1 or 2 of the original affixes on the Legend that I am crafting, it will retain it’s Legend status.
Quartz: use Kyanite instead, it removes most of the affixes on an item, but only one at a time. only use Quartz if you are trying to remove an affix Kyanite can’t. because it can remove from 1 to 6 affixes at a time, you might end up having to use many items until you get the results you want.
if you go to this thread, it is short, but there is a good answer to the question. hope this helps you in future crafting endeavors.