All very informative, I had some quibbles.

While it is true that cheap and expensive FPGAs exist, an FPGA system to replace TPU would not use a $0.50 or even $100 FPGA it would use a Versal or Ultrascale+ FPGA that costs thousands, compared to the (rough guess) $100/die you might spend for largest chip on most advanced process. Furthermore, overhead of FPGA means every single one my support a few million logic gates (maybe 2-5x if you use hardened blocks), compare to billions of transistors on largest chips in most advanced node —> cost per chip to buy is much much higher.

To the second point, afaik, leading edge Versal FPGAs are in 7nm, not ancient also not cutting edge used for asic(n3).