Taiwan used to be the actual seat of the Chinese government until Mao's communist revolution. Chai-shek and Mao had a ceasefire to deal with the Japanese invasion of the mainland during WW2. Once the Japanese were repelled by the coalition and the US, Mao immediately stabbed Chai-shek in the back forcing him and his forces took flee to Taiwan.
So you are correct: Taiwan is China. But it's Taiwan that supposed to be in control of the China, not the CCP.
Taiwan like Crimea for Russia, was always China's. It always was until British / Japanese colonist used it as a siege point.
To be specific:
Taiwan used to be the actual seat of the Chinese government until Mao's communist revolution. Chai-shek and Mao had a ceasefire to deal with the Japanese invasion of the mainland during WW2. Once the Japanese were repelled by the coalition and the US, Mao immediately stabbed Chai-shek in the back forcing him and his forces took flee to Taiwan.
So you are correct: Taiwan is China. But it's Taiwan that supposed to be in control of the China, not the CCP.
And that’s why China should be called West Taiwan at every opportunity.