Death Strike's heal working with Threat of Thassarian is a bug, but it does turn out to be a sizable heal. It's pretty notable. Since it heals twice, you can consider it a +100% healing bonus from a single Death Strike. Blood's talent for that increases the healing of Death Strike by 50% with 2 points in it. So, basically with proper talents, Frost's Death Strike heals at 200% value, while Blood's Death Strike heals at 150% value. Yes, Frost can Death Strike more often, at approximately a rate of 1 extra Death Strike every 20 seconds or so, which is 3 per minute if the "rotation" is done perfectly. However, Blood also has Rune Tap as another heal, and Vampiric Blood which temporarily enhances the DK's self-healing by 35%. As far as I know, Blood Worms are bugged, so the actual healing difference between the two specs, currently, is not that large of a difference -- the difference is much smaller than what it should be.