Some legendaries demand their own builds and do poorly in traditional builds...sure its not necessary but some items are not better than alternatives in other builds, just average.Quote from Doniazade
By that logic no piece of gear is necessary for any build. Wand of Woh isn't necessary for EB builds, it only improves your damage a bit!
You said in the video that the bracers don't matter which is plainly wrong. Strongarms are a massive group performance increase (the entire point of the build) and are also common enough that it is highly unlikely that you won't see them by the time you're going into T6.
Wand of Woh (ok its a wand it will be fine anywhere but its a waste in any other build besides the Woh build)
Myken's Ball of Hate
Velvet Camaral These two make your obvious build one of two electrocute runes..very specific and unflexible build but pretty damn effective as well.
Light of Grace Ray of frost is now piercing.
As with all of these, none of them are required to do the build...you can run electro or EB without mykens woh RoF without light of grace....but having it dictates your build a certain way if you do decide to use the item.
stormarm doesnt really do that, a LOT of things proc knockback.
Getting a perfect taskers on your non-pet WD or non-sentry Demon Hunter...time to swtich?
Strongarm bracers are just a bonus and arne't really required anywhere...they dont proc on the RG anyway (or anything too large to be knocked back...) They're fun to combine with an Ess of Johan but again you can't really base a build on that either