I think you are discrediting the effect secondary stats play, especially as they ever increase in value. Just because as a normal raider I'm around 355, doesn't mean that a mythic raider around 375 is only 8-10% stronger than I am. Just looking at the Zul encounter, my 95-100 percentile parses account for 16k-18k dmg for 375 (mythic) 100th percentile is 32k-36k.
I think the biggest advantage is the proliferation of high level gear. Having a choice between multiple sets of Azerite @ 355+ makes a huge different, especially when someone who is only doing normal/heroic and not as serious doesn't have that choice. An azerite trait gets changed and there goes the collected pieces.
Still I agree that it still seems like Blizz is "making it rain". An issue is that it's because they've added so many end game activities, and people simply won't do them without incentive. You bring up Vanilla, but really there were only a couple of crafted items, and then a progression path of 10 man dungeons into the raids. There was no reason to go back once you supersede a progression points gear.