A player could operate strictly by that advice and do ok, certainly. Where I intended my point to lie was in that the earlier poster's comment might be best taken as a guideline rather than a rule. But then again higher item level gear oriented towards a role is
usually going to be better. As you noted, different circumstances will benefit more from different itemization priorities.
Even so, there are some outright exceptions to the 'go for maximum item-level possible as long as they are tanking items' despite itemization. In the case of the two trinkets I listed earlier, the 271 is better in virtually every circumstance than the 359, with the sole exception being in a fight where the tank is expected to generally remain below the 35% mark in which case the greater uptime of the valor trinket's proc brings it back on par - and even then, no better. And sometimes gear can just be absolutely horribly itemized despite item level, as
Corpse Tongue Coin was for really all but one fight in its concurrent content.