I am using set items now and the difference between with and without is HUGE.
Does all end level game builds in Diablo 3 use set items?
Is it possible without set items?
Background:
I used to be a level 180 Diablo 3 barbarian. I used barbarian because I want to leech. I just want to survive and let someone good deal damage. I've been playing for a long time and never got past torment 3. Before RoS I did less than MP 3.
Then, long story short, I tried set items.
Now, I can solo torment X easily.
Best Answer
Yes and no.
Granted, class sets are designed to be end-game gear, and are a natural foundation for efficient builds. Most builds use full class sets.
But, first, not all of them. I can't say for every set, but there is at least a 4-piece Raekor speed build that sacrifices 6-piece Raekor's bonus for several select legendaries that synergize with 4-piece one.
And second, there is a "no-set set" - Legacy of Nightmares - that greatly boosts your damage and survivability for every Ancient Legendary item, as long as you don't have other set bonuses. This way, (with some dedication to farm all those Ancients) one can truly make their own viable build. Truly optimized LoN builds are often better than set builds (but then you are cornered into using those specific Legendaries the same way you are cornered into using a class set).