The thing is that you don't have to -.-. Something like twilight devastation doing 10% of your dps will be obvious upgrade in comparison to some other crap by hitting a target for two minutes. There are some not so obvious but YOU DON'T HAVE TO. You choose to to be "the very best". In vanilla or TBC you would be wearing ilvl 128 ring instead of ilvl 141. Why? It's a tier higher drop! Were sims available then? No. But there were plenty of people doing math and putting guides up.
The moment you use 3rd party site for gearing guide in an RPG is that a failure of the game company? Because then it is every damn RPG ever starting with Old School Runescape gearing ending with current WoW. Because no casual will ever do maths and tests on gear for hours. They will go on icy vein and check out most optimal rotations azerites and other crap there. Like 12 years ago. "Do I keep my t4 4 set or do I go for t4 2 parts and have this new non tier set helmet on me!?"
THINK MAN!