Build Guide
I highly recommend to use SWK+Sage's build with 2.4.1 SWK buff:
Put Inner Sanctuary and use Cyclone Strike to group enemies around elites on it. Cyclone Strike also procs Seize the Initiative so you get 30% IAS. Keep in mind IAS boosts Mystic Ally's damage includes its active one(only Cold rune), so StI is huge damage bonuses to them.
Hit with Blinding Flash to gain damage bonus and proc Relentless Assault. Relentless Assault is multiplicative damage bonus so it's huge damage boost.
Check you have all damage buffs(Forbidden Palace, Cyclone Strike, Blinding Flash, IAS from StI, Dashing Strike), then activate your Mystic Ally. You can one-shot an elite pack in almost all situation, so you can get In-Geom proc instantly. Spam your dash and find another elite pack. Ignore all trash mobs unless you need to fight them (like 1% for RG).
If the elite has some CC affixes, use Epiphany.
If you aren't geared well and luck some damage, use Way of the Hundred Fists: Assimilation instead of Inner Sanctuary and switch Endless Walk set with Focus/Restraint combo. stack Assimilation buff before activate Mystic Ally.
Overall you can farm 800+ DBs/h.
I use the same build for farming T10 except I use Endless Walk set and CoE instead of Bastions and Hellfire. For GR I put on Crudest Boots and Inna's helm (I use Sage's helm not Sage's gloves) and cube Spirit Guards and either Zodiac or Unity depending on how high of a GR It is.