That is what he's saying.
Self-healing is a non-trivial part of our overall survivability, and the only method of improving self-healing is increasing HP pool.
Basically, after the 30/45/60 point (roughly), endurance and mitigation stats have equal value in terms of survivability contribution, and so you want to stack them evenly. However, the way gear is itemized actually carrots us to stack a lot more endurance than mitigation. The 27B mods have a substantially higher stat budget than the 27 (unlettered) mods, it's just that the stat budget is devoted primarily to endurance. Since endurance is of equal value to the mitigation stats at this point in the DR curves, the 27B mods provide a substantially higher survivability contribution than the 27 (unlettered) mods.
The same is not true of enhancements though. The low-endurance enhancements have almost exactly the same stat budget as the high-endurance enhancements. Thus, here you're better off stacking mitigation over endurance. Overall, your mods should all high-endurance low-mitigation (27B), while your enhancements should be low-endurance high-mitigation (Bastion and Bulwark).
Regardless, the effective difference is minute, and KN's suggestions are predicated on the idea that you are gathering and spending Harnessed Darkness stacks as quickly as possible. If you are not good at maximizing your HD gain/spend, and/or you just don't give a hoot (which, let's be honest, many tanks, even serious raid tanks, don't), you're not going to be shockingly more squishy by stacking additional mitigation.
This is a very important point. If you have around 26k HP and your combat logs on an average boss fight show less than 200 HPS (including proc heal relic), you're probably not managing your self-heal ideally and my advice is not applicable.
Edit: KN is wrong about one thing, however, in that Assassinate has a 10% boost to Accuracy (due to the isSpecial flag). This does nothing to improve the value of Accuracy rating however.
Interesting. Given that bosses have only 10% defense though, wouldn't that indicate that special attacks should almost never miss? Combat logs don't seem to support that. I assumed it was only a 5% boost since my Spinning Strike seems to miss 4% of the time on average.