As some, as in, 'certain required set/Unique items' do not IMO determine the success or failure of the build.
However, a couple of things do crop up, as you mention.
Life Regen too, though Life Leech can be had in so many different ways now, I don't see that as a problem.
If I don't find a Kuko, no problems, there is always Wizendraw.
Piercing: without a Burrito or a Razortail, it just means progress is slower.
Holy Freeze: agreed. Having done that before, I have chosen to go BA with my Rogue_Ranger and may have to supply my own HF flashing now and again. My gambling aim will be circlets with +offensive auras or + Paladin skills. "That's where my money goes . . ." As an addicted Gambler, I may load up on some Find Gold charms as I get into nightmare, just to subsidize the habit!
Six Socketed Bows strike me as a crucial find to give optimum customization control for the Ranger in Hell difficulty. Once I get to level 24, and start using Holy Shock, my Bows will be socketed with damage other than Lightning. (Wont Turn Down a Sky Strike or Gold strike Arch, though.
My aim is to be able to kill anything, anywhere.
Diablo in Hell:
Aye, rather than go bow only, my second attack will likely either be knives thrown, or jav's thrown. I expect a VERY long fight with him, unless in a group. Lack of a summonable means that Fast Run Walk will be a critical equipment need before I attempt tho take him down, should solo be the answer.
Shield plus Javs, Holy Shock, patience, and pots strewn all over the CS floor.
And about 30 minutes to an hour to burn.
*Crosses fingers and hopes for a big time poison charm to drop . . . *