A some questions might to say

[Golem]

Eternal Items double the values of affixes. it does not double the values of Mythstones or Crystal affix values. you would need to find an Eternal Item with the affix you want, and it will be doubled value. the values are usually a random value higher than the maximum Legend Items value up to the maximum value possible on an Eternal Item.

Bad luck? Crystal affix weaker than epic affix

for the HP & MP on hit, Crystal only doubles instead of triple, so same value as Epic on Eternal Item. from +250 to +500 instead of +750. I think there is a game balancing reason for this. Edit: also, Obsidian can be used to improve your Crystal Affix now, not just Diamond. and only a few Crystals can be used on Eternal Items.