It shows Three Things:
1. Kid + Law aren't near Big Mom's Level, they are still Far
2. Kid & Law are prepared to do anything so that Big Mom is Stalled
3. There is No Confirmation that BM is going down this Arc, that is just your Headcanon
Big Mom is a Character that Oda created way before he started the Manga & before he even added Shichibukai & other Side Characters
Her Story has always been part of Original Plot. While Supernova are Characters which Oda didn't Plan for until Half the Story.
They will definitely have Big Roles, but not enough to change Big Mom's Main Role & what Oda planned for her (+25 Years ago)
Big Mom's True Role won't be explored until Final Arc
Fate chose her to be born with Protected Body, that's because she is Important for The Dawn, just like Luffy or Momo or Shirahoshi ... etc
Big Mom cannot be put down, she can only be Stalled or Temporarily Stopped