I think Jennie took the lead in answering questions during the Rolling Stone's interview, which is why they labeled her as such but tbh I don't see her as a leader
Rosé or Jisoo are always the one who speak for BP on award shows and red carpets. Rosé is a much more eloquent English speaker than Jennie imo - Jennie is not as good at expressing her thoughts and sometimes phrases things awkwardly. She does this in Korean too, and I think it is not a language thing but a her being awkward thing. As for in SK, Jisoo's speaking voice is picked on by Koreans but BP korean fans and translators have said she is very well-spoken and the best out of the group when it comes to the actual substance of what she says
In addition to being the one who speaks for the group, I think a leader is also kind of the person who looks out for the others. Jisoo is clearly the one who does this in BP. She seems to be close to everyone, and she's the only person who showed up at everyone's solo schedules even when she was super busy filming herself. I used to think her and Rosé were distant but now they seem to hang out the most out of everyone when the group is in hiatus
Everyone in BP except Lisa has some leader qualities - Rosé is the most well-spoken in English, Jisoo takes care of them the most and is the best at public speaking in SK, and Jennie is the one who mostly takes charge in English interviews and communicates things with YG. But I could never see Jennie as the de facto leader of the group as RS suggests so it makes sense to me that BP doesn't have a leader
