He was talking about using DPS armoring/hilt/barrel and power crystal on a tank. A competent tank doesn't need any DPS gear, and I used the shadow as an example. About the "caps", they are just urban legend for the tanks. The point of gearing a tank is finding a good compromise between the different bosses but, most of the time, gearing for the hardest boss.
Every single boss is different in term of mitigation, and they all have a different BiS stats. Defense, Shield and Absorption are useless against Kephess the Undying but you need them against The Terror From Beyond.
A tank without using those things requires using taunt in their rotation to hold aggro against top end DPS, a tank with them does not while requiring no additional healing but dealing more damage. If anyone believes the additional ~2k hp you gain from using high END armoring/hilt/barrel/crystals, then that is the way you should play. The difference in performance is so negligible that it borders on moot. I personally do not feel that the increase in TkT self-heals outweighs the freedom to hold back taunts and allow my dps to go crazy a little earlier, purely personal preference. Though the lower health (25.1k) would require me to adjust my gear if I ever chose to move into 16M content, those who stack more END would not.
Soft caps are not urban legend, just a point at which DR make it more advantageous to look elsewhere to invest points. The fact that some Ops Bosses favor M/R over F/T attacks (or vice versa) is really independent of the "point of gearing a tank" which also does not largely change based upon who the hardest boss is. Tanks realized since SOA that it can be advantageous to carry a set of DPS gear (even PVP gear) for bosses that are completely F/T, but this doesn't alter the philosophy of developing a tank. The variety of bosses doesn't serve to require any change in gear management but serves as an avenue of mastery of other cooldowns/abilities that cover for when gear fails.