I'm aware of and agree with your first paragraph. And the US does use proxy guerrillas to undermine it's rivals. But these proxy guerrillas are secularists. In Afghanistan, it was the secularist seven party alliance, not shariah advocates, they supported. In Kosovo, it was the secularist KLA. To combat China, they're relying on Han, Taiwanese, and Tibetan dissidents.
The US is against Islamists, universally, because shariah statehood means opposition to American foreign policy objectives on behalf of its energy corporations and Israel. The world is divided between 2 camps as far as states, the NATO-MNNA vs the SCO-CSTO mainly.... but there are non-state factions, aiming to become states, that oppose both, namely Sunni Islamism. They work for neither America, Europe, China, or Russia. Zawahiri wanted to hit China because he's a pan-Islamist and he resents Beijings transgressions against Uighars and support for secular despots in the Muslim world like Bashir, not because he's worried for the well being of the dollar or the American naval fleet in the Pacific.