Problem with that build is lack of move speed which is one of UB's many strengths.
indeed... speed is one weakness to my ub build (but countered in a very big way by poisoned dagger (20% chance on hit to reduce movement speed by 25% for 8 seconds) when you can choose that over BotF). I'd still take the loss of health per second for the benefits ooze provides. I lose 20 hps, but enemies take 35 dps with an attack speed reduction of 10%... once I hit level 4, I'm losing 30 hps, but nearby enemies take 70 dps + 20% attack speed reduction... and so on. OR, at level 2 I could get inner beast (3% move + 3% attack) or again at level 5 another hit of that (7% move + 7 attack), but its not quite worth it by comparison. Boots of speed alone would make up for the movement bonus you got out of 2 levels of inner beast. So, by the time I'm level 4, my opponents can't hit me as fast as I can hit them (20% slow down), they take 70 dps for every second they are fighting me, and I can spit for 800 damage. When I hit level 5, I get grasp. So, its usually spit, grasp (so the damage takes) hit and spit again if possible.
I personally don't think UB is OP. Like someone else mentioned, any dg that is constantly fed kills becomes OP. The only thing that probably needs addressed is Acclimation (level 15 skill). Everything else seems very well balanced to me on UB.