What is more important for running HM TfB is not that you have all 61 mods and Augments, but how you are optimized. Certain setups raise a red flag that the person is not on top of their class when picking what shells/mods/augments to use.
While some classes set bonus is weak, some make a huge difference. When I see an Arsenal Merc with no set bonus, I know they will be trouble. Loosing that free Rail Shot on my Merc means I have to use Rapid Shots more often to get rid of heat, thereby loosing DPS. When you see a Jugg tank with 29K HP because all their augments are Endurance, it makes you question their skill as a player.
I certainly does not mean you will be unable to run the op, but the fear is that the rest of the team will have to work harder to make up for your deficiencies. Like my example of the high HP Jugg tank, the healers will have to spend more time healing that person because their mitigation will be less. You heal HP of damage, not percentage of total health. Less mitigation means more HP of damage. Large HP pools defining a tank is EQ1 times.
I would totally disaggree on the tank thing. I think its pretty much common sense that primary stats for a tank are 1) damage reduction and 2) HP. There is no better way to mitigate dmg than by those 2 stats. Forget shield and defense chance since they will not mitigate consistently. A tank stacking endurance, thus increasing his HP is doing the exact right thing. Hence your reasoning is pretty much off-base.