Its a multi-facesd issue, Im going totally off memory so i may be mistaken with a few things
1)I think youre partially right people are pissed that there was another opportunity to add legit high elves and they don't like the Velf compromise.
2) The story we got has made Blood Elf lore awkward. Since WC3 we understood that Blood Elves as a society have a very liberal use of magic (ideal warlock race)...this carried through all the way up to Legion. Now with the Velf story quest we see that the Blood Elves have a fairly strict system of what magic is okay, banishing shadow magic users from their land. This lore is totally out of left field "ie an asspull" we saw no build up to this and it was sudden all in one quest. Why don't they just prevent elves people from visiting the sunwell? Umbric and friends werent doing anything insane with old gods so are all practicioners of shadow magic banned? Whats happening with blood elf priests? What about warlocks they use shadow magic? How about users of Fel magic and demon summoners, are they all banished as well?
3) They objectively have significantly less lore than vanilla gnomes and tauren (Gnomes were in the lore since WC2, and Tauren since war3 with an entire zones of questing in WoW)...but I'd agree in saying that there were more appropriate race choices for the vanilla alliance than gnomes. That being said the playable Velfs only have a single quest line of lore, Alleria isn't like the PC void elves so I would not include her.
I don't believe blizzard added blood elves to the Horde because of Chinese players, no idea what youre referencing here (source?). The BC Draenei were a major retcon because blizzard wanted playable Eredar. SOURCE
https://www.youtube.com/watch?v=kei61shkWhU