>China's SMIC is very far behind

I think you misread the thrust of this comment. Commenter was likely alluding not to R&D, but an amphibious invasion, as to how it would end up being China. Obviously I don't know how much of that infrastructure would persist to be carried off after that invasion, but it would reasonably be considered 'lost' to the US.

Taiwan is right across the border from China. At any point, they can invade and take over.

Right across a strait*

An amphibious assault against a prepared enemy is never easy or straightforward. China doesn't yet have the necessary logistics ships to be able to supply a beachhead so Taiwan should be "safe" for at least a few years.

yes, although the subsidies supply to anyone who builds fabs in the US, including TSMC.

Indeed, the point is to create jobs in the US and to, in the long run, lower the risk of a complete takeover of TSMC in case China invades Taiwan.