Even if the leading US labs could agree amongst themselves to a coordinated slowdown (and this would likely run afoul of antitrust law), you still have Chinese labs who will catch up to the frontier eventually. To solve this, you'd need some sort of international agreement.
That's why Dario and others are saying loudly that we should pace the frontier in hopes that our political leaders will take up the issue and do something about it. We'll see if that happens...