It's not either/or.
ZB+ is crowd control in the physical sense while FVM is crowd control in the spiritual sense, so ZB hampers movement and give ranged dice (both defensive and offensive) as well as increase initiative, while FVM is more about hampering people through their resolves and so on.
They are both Crowd control abilties that vie for Ling Qi actions, the arts simply don't synergize because Ling has to choose which one to activate and FVM is currently the superior option. When Ling Qi needs to put a person down she has to rely on either pitiful knife throws or archery which doesn't currently have a big damage spike.
Anyway, about ZB. ZB is amazing for our dodgy ranged support build. Its passives give us +ranged, +ranged def, and + initiative (which is awesome). It's arts give us pushback and a projectile shield, Against the Wind is a great debuff. Guiding Zephyr would be great if it was instant.
And that's really the big problem. It's dice are limited right now because it's only a mid-red art. AGtW and GZ not being instant is really really bad. If they were instant we'd be able to actually use them with our other techniques. Right now we have to choose between AGtW and GZ, so we pretty much always use AGtW because that's the best option. If we could use GZ to buff our dagger throw when we're procing AGtW though it would be way better - and a more usable GZ would also significantly improve our ability to throw stuff in while we're playing. Being able to stack ZB on top of FSA would hugely improve our ranged game as well. ZB is one of the best options we have to shore up and improve our core style.
Also, it doesn't overlap with AC. AC is a melee technique. We are primarily ranged. We have allies who also do ranged (i.e. Xiulan). ZB is great for us.
I mean, maybe it was talked in the thread somewhere but I didn't see any guarantee that the upgrade art would simply improve ZB instead of being it's own thing (That requires it's own meridians), and for all that talk of Ling being a ranged fighter most of her techniques require her to be within 30 meter radius of her opponents which is nearly her speed if she also uses SCS which kinda suggests that it's also her opponents range as well. Only one of Ling's allies is ranged (Meizhen, Han, Suyin and the spirit animals are melee based and even Su Ling is trying to switch to melee arts) so that argument falls kinda flat.
I agree that ZB is currently isn't pulling it's weight but I am not convinced that putting so much effort in it is worthwhile, especially when there are other tech that do help Ling and shore up her other weaknesses.
Also a dumb nitpick, but using the Black Ichor Elixir without knowing the art hidden in the book seems like a waste, even if the art turns out to be useless for Ling Qi.