So Source's brand is kind of in the toilet right now with how things went down with GFriend. I'm not really sure how GFriend fans or the GP will react to a new gg debuting with them anytime soon. And with the way the 4th gen gg market is filling up quickly with monsters like Itzy/Aespa/StayC/Weeekly/etc, I feel like groups are gonna need something big to standout. Being BTS's first female juniors would definitely create some hype.
It obviously isn't as easy as just jumping over to a different sub-label -- SM would probably need to dissolve -- but I do think being a BHGG would lead to more success than being a Source group would.