Dual lash by itself isn't so bad. Sure it's kind of annoying to get yanked around the board by the other player, and it can be used pretty effectively to setup or delay assaults. It's also got the off chance to pin a unit which may be helpful every now and then.
The real power of lash is it's synergy with templates. double lash princes aren't so bad. But 2 lash princes with 9 obliteraters is down right mean.
Using that 2d6 move to clump up a unit and make it a nice juice target for templates is where it's border-line abusive...but thats part of the fun of running it