Deathgrip Reapers are so powerful because the "Warriors cleave with their attacks" mechanic is ADDITIVE with normal Reaper cleaves, creating a huge AOE for each attack.
A major reason Skeletal Warrior builds are meta for Minions right now has to do with the crazy AOE Reapers are generating. It turns out that the Deathgrip text "Warriors cleave with their attacks" is NOT redundant with standard Reaper cleave attacks; it is ADDITIVE, so Reaper attacks cover a HUGE area, as seen in the video. This is reminiscent of S11 and S12, where Ring of Mendeln fell out of favor in Hand of Naz builds in part because its AOE was so small compared to loading up on Shadow damage for the higher-range Naz Shatter mechanic.