You're acting like international treaties (or cartels) don't exist. Yes, these are structures where parties have incentives to defect, and we counter those by creating incentives not to, with checks and sanctions.

Additionally, you don't need all the leaders of the world to agree to anything, you only need US and China.

Additionally x2, if you agree with the common stance that China makes the vast majority of their progress by distilling US models, you don't even need them to agree to anything.