What is your take on Armor, Evasion, Energy Shield for Hard Core?

I have not played hard core yet. Still trying to get a better understanding of synergies. I play as Mercenary.

Basically, Crossbow requires STR and DEX. Which naturally implies going armor/evasion combo gear. Needing to raise both in order to use your weapon means you won't be able to put additional points into one of them to qualify for the specific gear. Such as armor or evasion gear only. Same for es gear if you can't put points into INT due to STR and DEX being needed for crossbow.

This is also coupled with convenience in the tree for class specific gear. Like armor/evasion for merc. So it seems that it would be most effective to stick to the gear of your class type. However, I have noticed multiple users suggesting that it is a better idea to spend points to venture further out and invest into raising additional stats in order to use a better form of defense.

So would not your natural available defense be the best option? Or is it better to invest in a different form of defense if you're something like a Mercenary?