I am pretty sure most you do not understand him correctly. What he says is: If e.g. 305 of a Mainstat is better than the amount we from legion items, it might be better to continue to wear WoD items.
Its because the op and you apparently dont understand how secondary stats arent weak. For most class they are worth 50-60-70% of agility. So once you hit a certain itemlevel the main stats of items dont keep up at all. Its not even that far, its just while leveling. My rings have 800-900 of secondary stats, agility on old rings dont come close.
The game has moved on from where agi/str/int were at LEAST double the worth of a point of the best secondary.
My second best stat is 70% of agi. My third best is... about 65%? I think? Can't remember. Long and short is, a WOD ring with 300 agi and a small amount of secondaries vs a Legion ring with almost 500 Vers and 500 Mastery... well, it's just no contest. My rings were replaced by 104.
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