I find it kind of unfortunate, that whirlpool outclasses many many melee skills. I started a bear druid and on my first crafted Axe with decent damage I received a whirlpool oskill by chance. It's a lot better than Rend. It has a bigger AoE, which makes farming easier, since you hit more enemies for better LL values. Especially so since you can just go ahead for a hit and run strategy, and that it's not only dealing damage in a cone. And when it comes to bosses or other non-moving targets, it also excels at peak damage, which comes mainly from the fact that Rend in melee range will always spread. Rend only excels at solo targets when you actually walk a bit away, so you can have all 3 thorn lanes on 1 target. But that doesn't work in melee range, which means you either have to make sure that the boss is at the very perfect sweet spot all the time, or you just go with whirlpool and kill bosses with ease. And all of that is coupled with the fact that I have less mana issues when using whirlpool compared to rend.
But that's not all. I tried whirlpool out with almost every class. It always excels compared to other melee skills. The only few exceptions are naginata assassin, where it still complements the build well if you go for Barrier strike, and any pounce like build. Pounce zon has the Great Hunt skill that excels at solo target damage for example. But Whirlpool still complements that build well when it comes to farming without pounce (if your damage is too low to be effective). Wolf Druid is a lot better/faster with its Pounce type skill as well and the unique mana mechanic makes it not that worth using whirlpool. Carnage is worse than Whirlpool when it comes to damage output against bosses. Regarding Barb, there was a video by aerial some time ago, which showed that whirlpool is better than almost all barb melee skills against solo targets.
So I guess what I want to say is: Whirlpool needs to be changed. The way it is now it outshines almost all melee builds up to a certain point, which makes melee builds feel stale pre-125.
Here are some suggestions to change it: Either by reducing the AoE or by reducing the amount of hits in the middle, or by adding a damage conversion. Or all of that.