WB was lynchpin holding up the balance and keeping everyone from acting recklessly, yes.
Shanks did nothing when WB was alive, sinking a few government ships is nothing.
SMILEs and Germa are both things that started when WB was already gone, and Kaidou stated he amassed so many SMILE user to start the biggest war. So the preparation for it started literally after WB was dead.
I did not say that the powerups would upset the balance, i said Kaidou and BM are less careful to stick to it since WB is gone. BB represented a fourth power that is almost equal, but he was and is not a WB, and while he prolonged it, ultimately the people in it do not care so much.
Also did not say the balance is gone, we literally have a chapter stating the Marines can´t quite classify recent developments yet, i said Gorosei stated it can not be upheld anymore based on the events that transpired since 2 years ago, which does not mean it´s completely over, it means the situation is so dire, teh result will be a complete power shift, which will break the balance.
Hence cleansing.
https://mangabeast.com/manga/One-Piece/0908-013.png
"roiling has not ceased since paramount war" -> WB´s death, roiling means unstable situation and uproar, ceased means it has continued since then. If the stalemate was just 4 equal forces, BB would do the job, it isn´t though, WB´s existence is highlighted.
"world´s equilibrium cannot be maintained forever" -> dire developments, upholding the balance seems impossible -> cleansing.
