Yeah, i'm not knowledgable enough to comment really. But i learnt WC/JJ/Aikido/Wrestling first, and to me, i don't really see any need to study BJJ, because the same principles apply, except it's on the ground and less room.
Basically like i said, i am a JKD guy, and once you have an understanding of movement, of anatomy(how to hyperextend joints etc), positioning, it's all the same in any style or any place you fight. Just need to know the concepts and theory. The rest are just little tips and tricks you'll pick up. The overwhelming concepts stay the same overall. It's like saying, if wrestling was incorporated into bjj in the 70's, then what's the point of learning wrestling? Sounds stupid when i put it like that right? I can say the same for JKD. Why learn anything else when JKD teaches everything?
It's basically about what those styles focus on, and in general that's what you get out of it. They might have standup, but the focus isn't on that.