This skill has just under 30 seconds duration at lvl 120 and isn't increased with buff duration. The defense and life are definitely useful but it starts at around 20 seconds at clvl 1 so the frequency of recasting, especially while leveling, is more of a nuisance. Would be better if it had flat duration that didn't scale with clvl and benefited from buff duration.
I ran a barb from lvl 23-90 last ladder using this skill. I quit after finding out that 1pt Iron Spiral (with cooldown) had better clear speed. It wasn't a bad experience while leveling but too slow to be used as a main skill for for farming anything relevant. Now with the "buff" its much worse for leveling. Not a big deal, assuming that later on it would be good but its unfortunately not. With a low slvl (Thul body armor) the skill has just over 1 second of duration. So for most classes the most overlapping will be around 3 attacks per second. With the reduced overall hits of the skill it can't "charge" up enough damage in the area to deal with packs efficiently. Later on with around a 3 second duration the skill hasn't improved. Yes it lasts longer so a player can stack more aoe damage but having to hit the same enemy repeatedly to do so lowers kill speed too much and the splatter damage feels underwhelming. Another thing I've noticed is that there is a brief delay between using gorefest and the guts appearing on the ground. I'm guessing this has to do with the reduction of projectiles of the skill itself. It reminds me of the delay shower of rocks has, but shorter. Most melee skills don't have a delay and the damage is at least immediate.
Regarding the math of the buff itself, Hits were reduced by 1/2 so the first 100% of increased damage makes up for that. The additional 80% is really only 40% because, again,it hits half as much. A 40% increase to gorefest that was dealing 25% wdm before is an additional 10% wdm, or 35% total. For comparison, whirlpool had its cooldown reduced by half and its wdm% was doubled. Thats effectively a 300% damage increase for Whirlpool where Gorefest received 40%.
I'm not sure what the solution would be. The recent trend has been to reduce procs in the name of "performance". Its possible that its viable in late game with the right gear and maybe the intention was specifically that. Idk. It felt more useful prior to this patch.