Pandaren Pheonix: unobtainable and no similar models
Mushan Beasts: galleon or bloody coin grinds
Furbolg Bear form for druids: Only through a, frankly, skuffed MT reboot and only the fel version
Tons of Weapons/Armor options that only drop from legacy content and on a slim chance and have no equivalents for people to get other than to pray it drops (or with the armagedon sword look alike, jump through convoluted hoops the require you to have an addon to even see how in game)
Cosmetics allow people to enjoy the game/experience the fantasy they want too within the World of Warcraft. I’m glad you have options available to you that let you fulfil that desire/fantasy adequately, but as you said, you only really pvp. Other communities like the RP community are much more affected by things like this than you would be.
You mentioned not liking how you need to ‘grind’ non pvp content to be able to play pvp right? Imagine your ability to do pvp in the way you want would require you to grind raids for years, praying for one, specific, item to drop, so that you can properly enjoy it in the manner you envisioned. That is what quite a few RPers are stuck with to fulfil a character concept properly.