Regarding of debutin Le Sserafim first than New Jeans, I it's based on the timing. Le Sserafim has 2 ex-Iz*one members, and from what I know Iz*one was a huge hit, arguably the 4th gen leader at that time. Their fans also very loyal which makes Iz*one's sales skyrocketed, at the top only with BP and Twice.
When the group was about to disband the fans are also do this funding to extend their contract and gained approx 3,212,770,000 KRW (~ $3 million USD). seeing the potential, BSH scouts 3/12 Iz*one's members, but only 2 agreed to join with him. To keep on riding the hype, he decided to push Le Sserafim first, as IVE (another group with Iz*one's ex members) just debuted.
It's only my opinion about this MHJ's claims. If I state something incorrect, please let me know because this case starts to confuse me lol