China is only still getting oil from Iran, because we allow it. China knows that. Venezuela and Iran partially tells China, the US does have influence over your oil shipments and you can't sanction proof your oil supply chain. Stopping China's oil shipments right now would just make oil prices go even higher, but we definitely could stop them.

As for Russia, yes there is still some European reliance on Russian oil/gas, but that isn't the only issue as there can also be concern over civilian casualties inside Russia with a complete collapse of oil infrastructure which could hurt some aspects of public support for Ukraine inside Russia and in the rest of the world.

Iran doesn't produce anywhere near 20 million barrels of oil per day, and only a tiny fraction of the 30% of LNG supply is disrupted, which will be coming back online within 3 years. You could argue that Iran might expand its attacks on all the infrastructure in the region to try to take more production offline, but their capacity to do that is shrinking every single day. Even if they did manage it, that would basically greenlight a multi-national ground invasion to end their regime for all time. So just like your arguments about the limitations Ukraine faces in taking out Russian infrastructure, even though Iran is a terrorist state and demonstrating how their terrorism operates, they are still fundamentally limited in what they can do without destroying themselves.

When it comes to China and Taiwan, you need to better appreciate that China has had a standing policy to take Taiwan by force if Taiwan sees itself as independent. Increasingly the Taiwanese population do see themselves as independent and they are arming themselves for defense.

China did not magically bring its population out of poverty, the US did that, by opening up to them and allowing them into the WTC (which they then abused). We thought it might liberalize their economy, which might liberalize their politics, which would pave the way for democratic reform. It didn't happen, but that was part of the plan. The other part of the plan was to increase the dependency of China on western supply chains, because this was part of the logic to stop world wars by making everyone interdependent on each other.

Communism is freaking awful, because it is never achieved and always seems to stagnate into a permanent state of dictatorship. It then sucks enough that it cannot maintain itself naturally, so it has to repress its population and heavily control information to simply prevent crumbling. The logic is not self-reinforcing. Therefore, it absolutely, critically is a threat to freedom around the world.

Technology advancement and resource access accelerates with global trade, so if one country goes rogue, that supply chain can be cut off reducing their incentive for war. China now sees that it continues to have many critical dependencies and its current potential is only achieved as part of a global trade network. Their sanction proofing will never be complete. The concern is that they may not care that they're at a disadvantage and do what they want anyway.