I don’t understand what you’re saying the mistake is?
You’ve referenced it several times and not actually told us what the problem is.
I’m not even sure what this means. The primary objective of any zone is to tell a story, is it not? I believe Zaralek has done that with the questline leading up to Aberrus.
And since when are rares the “primary objective”? They’re hardly rares anymore (not like they were in BC/WotLK), they’ve been used as cosmetic grabs for several expansions now.
Were rares the main part of Tanaan Jungle? Of Zereth Mortis? of Nazjatar? No more so than Zaralek Cavern is. I consider all these zones to be very similar - which is objectively true because they all serve the same purpose. Unlock a new faction, tell the story about getting to the new raid, and offer some treasurers/rares/cosmetics to hunt down if you choose to.
Not sure what the big mistake is here, to be fully honest.