I said it's slowly becoming meta worthy not meta worthy at the moment but my point is weakness is part of the game there's no need to downgrade a card just because of weakness even if it's a bad one and not to mention Banette GX has resistance to Buzzwole so it's not a bad card Buzzwole GX is also meta and it will get out of control with the new ultra beasts support so Zoroark GX players will hide under a rock (no pun intended lol) in the next meta. And not to mention one more thing you can also pair up Banette GX with Zoroark GX therefore Banette GX is a good card.
Ok, so reasons why Banette-GX is bad other than its weakness to dark:
a) In Standard you want to be using your supporters and not discard them because there is no easy way to get them back later. Puzzles will also rotate this September. You have Pal Pad, but that forces you to shuffle 2 back, which immediately lowers Banette's damage output by 20.
b) Discarding stuff in Standard quickly is not that easy unless you're playing at least a 3-3 Zoroark line; therefore Banette's damage output will take forever to max out and it will get killed before it can contribute anything to the game. It's not even like Trashalanche where you can just use Garbodor as a late game attacker for huge amounts of damage, or at least enough amount of damage to OHKO a Lele or something else to get you the win.
c) Which leads right into the next problem, namely that it has a very low damage cap, especially compared to some other GXes. It doesn't matter that it only needs 1 basic energy because it can't do anything with it because, again, it has a very bad attack. The GX attack (Hollow Hunt v2.0) is good though, but Banette managed to make it worse than the Decidueye version - using it ends your turn, and while Decidueye can usually tank a hit with 240 HP, Banette with 190 (and again, with Zoroark weakness) will probably won't be able to do that. Even crap like SLG Hoopa OHKOs it with a Band and it even walls it.
d) The ability is very situational and you can't even spam it to help you get KOs easier - like Feather Arrow, for example - because Banette needs to be your active in order to use it.
e) The resistance to Buzzwole doesn't matter because good Buzzwole decks just plow through everything due to having a ridiculous amount of damage boosting cards at their disposal.
f) You can't play it in Expanded with Compressor because Zoroak is disguistingly strong in that format and it will OHKO Banette even without weakness. Having dark weakness means that the Zoro player needs to put in even less effort to get rid of it. And playing a 2-prize attacker in Expanded with a damage cap of 130 (160) who only has 190 HP is just generally a bad idea because Expanded Turbo decks eat such things for breakfast, and mill/stall decks like Wailord, Toad/Seviper and Sylveon just laugh at you.
The only way I could see Banette being used is as a tech against Buzzwole in future Zoroark decks, if, after EVO Mewtwo and Mew EX rotate, we don't get anything better than Banette for this purpose. (And Trashalanche is already here which is imo better for this but whatever.) It's not even very good as an anti-Buzzwole tech, because both Mewtwo and Mew EX only take up 1 slot in Zoro decks and they both share the DCE attack cost.
You'd either have to run a 1-1 line which is unreliable and you might not be able to get it out at the exact time when you need it, (not to mention that killing off an unevolved Shuppet will be really easy because it will probably have like 40-50 HP) or a 2-2 line which takes away 4 slots and they will probably become dead cards in most other match-ups, not to mention that you also need to find space for either at least 2 Psychic or 2 Rainbow.
And even if you OHKO a Buzzwole with it, it can OHKO Banette back with Beast Ring + Choice Band + Diancie or with its GX attack if the opponent hasn't taken any prizes yet. There's also Lycanrock (who will probably become the main partner again for Buzzwole after Garbotoxin rotates) which you can't hit for weakness with Banette.