Recently I found myself in a predicament. As I was trying to explain to a person who's been out of this game for several years how blood tanking works... I had to spend several minutes explaining the whole deal. And like the title says, doesn't the whole set of rules and conditions around the core devices of blood tanking seem a bit too much of a clusterfuck?
In essence, blood DK tanks using a strike that deals damage to an enemy and heals you for percentage of the damage you have sustained from non-player sources during the preceding 5 sec (minimum of at least 7% of your maximum health), cannot be parried, and each time you heal yourself with it while only in Blood Presence, you gain a percentage of the amount healed as a Physical damage absorption shield, and this value is increased by a mastery stat. In order to actually be able to take advantage of this mechanic, you have to use add-ons like Bloodshield Tracker.
In comparison, Warriors tank using shields that block 30 or 60% of damage with certain chance depending on mastery. Note how this takes only one short sentence, while DK's one took four lines of text.
I was thinking of something more simple. What about the following:
Death Strike healing for a fixed amount, say, 10% of DK's max health.
Mastery would increase the heal depending on how low DK's current health is.
A passive ability would allow him to store overhealing received from his own abilities for 5-6 sec in a manner similar to Vengeance (so that it neither adds up infinitely nor vanishes all at once).
Don't be too harsh judging this concept, it's very rough, but I offer it as an alternative to the existing mess (a working mess though, I have to admit).