Agree that deaggros are broken - on my chanter bewilderment is enough of a deaggro to keep me from ripping hate. On my scout, I hit my DPS chain at all and I have the mob in instances about 80% (I usually start it after mob is about 20% down and I have like 10% hate and have to stop the chain or pull aggro) of the time. So I just don't touch the chain buttons (IE: double up as a brigand) unless I have a really good tank.
Is it cause of bad tanks? A lot of it, yeah. But there are way too many bad tanks in the game, especially on low pop servers. 