If these were chess pieces, then yes, BI vs Zion is an easy win for Zion. But they're not just chess pieces. There's a gigantic human element to it and that element makes it to where the franchise can't trade BI....especially for a rookie.
Griff gets the human element. He has made his entire brand the human element. Pushing the FF for family mindset and saying they're trying to change the culture in NOLA. And he's been super successful doing it. Free agents actually want to come here, now. Players are happy getting traded here and devastated getting traded away. The first to buy into that culture was BI. It's a mistake to not see how much of that family culture he is. If they trade him away, the entire family element brand falls apart. So they just can't.
Zion on the other hand has been the biggest threat to that culture/family atmosphere. Any time that element is in doubt, it's because of something involving Zion. He's a great chess piece but as a person, he has been a constant thorn in the franchise's side.
I think Griff trades Zion way before BI to protect his brand.