I thought the interesting point is not that the mainland can overwhelm a small island off its coast, but the likelihood of a messy escalation and stalemate. The logic that defending the island requires taking out integrated air defense radars on the mainland and the implications of that seem pretty sound.

During the Korean war the larger mainland forces took everything except Busan, a port on the south-eastern side, but the US still rolled it back and today we have South Korea. On the ground, the reality of even a few weeks of that kind of urban all-out war are truly horrifying.

The US and Taiwan had an explicit security guarantee treaty for 25 years

https://en.wikipedia.org/wiki/Sino-American_Mutual_Defense_T...

...with the rise of China that mutated into the TRA

https://en.wikipedia.org/wiki/Taiwan_Relations_Act

which is more ambiguous, its basic idea is maintain the status quo. On the ground, forces are stationed in Okinawa to deter mainland aggression.

In recent years the likelihood the US would in fact jump in to defend Taiwan seems to have increased, eg, reliance of US tech industry on TSMC, and Trump-era anti-China rhetoric. At the same time Hong Kong shows the mainland tolerance of democracy has dwindled.