Let’s say for the sake of argument, that’s true just to shortcut this: the PRC is also not party to the Rome Statute. Neither is Russia if you’re wondering. The largest military of a country party to the Rome Statute and the largest financial contributor to the ICC is Japan. Good luck.
The ICC is only truly relevant today as a means of imposing justice on smaller countries without the rule of law or the power to protect themselves from larger nations. Not quite irrelevant, but certainly not a powerhouse in real political terms.