That's just one assumption, its also long been assumed that the massive increase in hash rate is due to some other chips being made that aren't publicly available.

Bitmain has no moat, if an American fab wants to start cranking out chips they can... and tariffs give them even more reason to than they had before.

The other variable not accounted for is the fab making Bitmain chips has to start making other chips because of China's lack of access to US chips

Agreed that pools and block templates are a concerning centralization vector, but I'm optimistic given all the solo blocks being found and things like Heatbit ramping up. I expect in ~5 years any appliance in your house that uses a heating element will have options for a version with a chip-based heating element.

Every houses hot water heater mining sats means every homeowner get to vote with hash rate which will make pools/templates more user-aligned and therefore decentralized.