Where is the power progression in a cosmetic item? Thats generally what rares are for now a days is a cosmetic loot pinata. If you want “power progression” you aren’t going to be killing rares, you’ll be doing mythic + and raids.
I’d also like to add as an expansion is sunset, the rares become harder to farm because you will likely never find them up/called out because they die in one hit. This is the case for late BFA, Shadowlands, and will be the case for Dragonflight rares because no one will throw up a PF to say they are up much less wait for anyone else to arrive before they kill it.
There is no joy in wasting 2 hours for something to respawn after someone else killed it before you got there. Only frustration that you could be doing something else. And before you come back with “Then why aren’t you doing something else?” Because any collector through and through will not want to miss the next spawn to try to get something they’re after to complete their collection.