I agree with some of your points but I'm not sure I can agree with your overall conclusion. Much like the majority of opinion pieces it's all subjective and might be wildly inaccurate.
For example, from my experience wPvP has actually increased this expansion. The combination of a loss of flying and the increased popularity of alts has led to me experiencing a lot of additional wPvP action especially around the entrance to raids.
Similarly, heirlooms have been around since early Wrath (ie at least 6 years now) and the experience I had then was that they actually led to increased player retention. Plenty of players who said they'd of unsubbed for a month or 2 rather than level and gear up a new alt were encouraged to stay purely because there was a quicker route to max level now. The last 2 expacs added what, 1 slot for heirlooms in the neck piece? Unless I'm grossly mistaken on that point I can't see it being a deal breaker that 1 new piece was added or they'd of quit years ago over it.
Gathering is nearly gone for sure, damn now it means I need to buy from players deliberately undercutting each other with stuff they got from their garrison rather than the botters who deliberately uncut everyone. It most definitely made gathering a less worthwhile profession however, at the least they should of made the battle pets from mining/herbalism only drop if you had the profession. Literally the only people I know who've had them drop are people who no longer have gathering professions.
Sure professions are time gated and mostly suck. Sure am glad that they never had stuff like living steel, titansteel, dreamcloth and many other things in other expacs on daily cooldowns which time gated the benefits you can get from crafting! Literally the only difference now is that you can no longer trade the items such as titansteel.
Customization would of been more exciting if it really existed. However the reality is that it never really did exist, just the illusion of it. Guilds with standards would often armory you before accepting you and if your reforges/gemming/enchants weren't up to the required level you would either get outright denied or told fix x/y/z and come back. People didn't gem crit for the potential at big numbers if it was their worst secondary and they could get 4x the dps increase by gemming haste. You weren't a spec that favoured crit/haste over all and yet decided to reforge/gem/enchant into pure mastery so you can be the most masterful mage/rogue/hunter in all the land for RP reasons. Most of the customizations that did happen were can I afford to gem full epic gems or should I just stick with blue gems til I get my BiS or hmm should I get the cheaper, serviceable enchant on my weapon or go all out on the best one?
Hunting for rare items is a minor thing really in my mind. I don't honestly know anyone who did it. Lots who were super happy to be farming Karazhan for the mount/pets/transmog who would celebrate if a Blade of Wizardry dropped and they could make a nice profit from their run as a result but last time I knew people to deliberately run an instance regularly for specific drops was old SFK for their twink weapons.