I think people forget that once they hit 60 they will be in the same situation as they are in BFA when they hit 120
Whats next ??
Also look at the end game of Classic/Vanilla what is there for the people who were not in successful raiding guilds ?
Classic end game -
Heroic Dungeons (these will become trivial over time)
Raids(Requires you to be in a guild with a relatively high roster count and active players)
Gold Farming.
PVP
BFA End Game -
Raids (4 Difficultys)
Dungeons (4 Difficultys with increasing rewards based on level )
Azerite Farming
Gold Farming
Island Expeditions
PVP
I think that the main issue is that World Content needs to be tougher in BFA and have a system that rewards people for grouping to do quests and such during their levelling process, Maybe a XP bonus to people who are grouped and within X distance whilst questing.
This is the main difference between the 2, World content is too weak and so therefore it does not feel rewarding to level through the content.
As you can see once you compare the 2 that BFA has far more end game things for you to do than Classic.
Once you have max level and all the best gear that is obtainable for your character what then ? Of course people will ask for more content and more gear to continue this experience and this is why we have ended up where we have 15 years later.
People will cry for more content so Blizzard will release TBC to provide more solo content for people to play and the cycle has simply repeated itself over and over.
Also as far as gear feeling like an upgrade , Lets see what Classic looks like after 15 years worth of items and 2 stat squishes, Its a lot harder for them to manage gear in BFA due to the sheer power creep of gear, So they could do a better job at managing gear, Maybe if they reset all stats to 0 with every expansion and then each expansion would have its own set of gear which is not useful in the newest form of WoW this could prevent useless items from past expansion ie… Artifacts from Legion being carried into BFA.
As far as Gold being useless in BFA, They do not require Gold for spells anymore but they have other outlets of Gold spending such as Mount,s , Professions, Bonus Rolls for gear, and WoW Tokens which allow you to pay for your subscription with Gold which was never an option in Classic.
Now I am intrigued as to what Blizzard will plan to do, In my opinion they should not have released it as Classic but redeveloped the whole thing and finally took the plunge and done WoW 2 but implemented a lot of Classic features into rather than lazily reselling Classic.