I'm not even arguing that you're wrong.
Your mathematics are sound.
GUN's and DRK's invulnerabilities will pretty much always require assistance of outgoing heals, while WAR's may require healing occasionally.
I'm questioning the relevancy of your statements to begin with.
The mandatory healing resources living dead requires will always be greater than those for any other tank invulnerability, due to it's very design.
In addition, you have to cooperate heavily with healers to actually make it's duration not suck, while naturally making the DRK prone to potential death in the process - two concerns no other tank must worry about at all.
Not to mention in extra light(Less than 4)group and solo play, Living Dead has zero uses for practical application.
Quite possibly the most embarrassing strawman in this thread.
The majority of healers are complaining because of a lack of options they can utilize during healing downtime during encounters.
I'd imagine most wouldn't want to heal more if the only reason to do so was to cater to the immense drawbacks of outrageously poorly designed skills.