WW Bugs ← That should explain it better than I can I think. TLDR: Whirlwind had two free hit checks at 4 Frames and 8 Frames before the weapon APS took over. These were not working as intended and were “bugged”.
If you had a two handed weapon at 6 Frame breakpoint, WW would attack at 4/8/14/20 Frames. If you managed to get it to 4 Frame breakpoint(which everyone could do prior to 2.4.3), you’d have 4/8/12/16/20/24 Frames or 6 Attacks per second. Now 2-H, from 2.4.3, is relegated to 5 Frames max and the 2nd hit check appears to have been removed so now WW with a 2-H at the 5 Frame breakpoint now attacks like so: 4/9/14/19/24 ← ~5 Attacks per second. That accounts for roughly a 17% DPS nerf(5/6 = ~.83) and doesn’t factor in the minor damage nerf for Whirlwind level 28 and higher(since they also changed the skill’s starting %ED and how much it increases along with starting Attack Rating).
Oh and being chilled, Holy Freeze and Decrepify now affect WW’s APS(didn’t before), meaning in the right situation, it can be lethal. Since a 2-H Barb can’t Frenzy to generate Skill IAS, they must rely on Fanaticism(nerfing their damage output from A2 Might + Pride). IK Set really got short end of stick on this too.