I agree with your general point but computers are weird. Attacks and exploits can have scaling properties much like other software. We can do something expens

I agree with your general point but computers are weird. Attacks and exploits can have scaling properties much like other software. We can do something expensive (say $200k attack cost) to break the platform and sell 10k $100 mod chips. The defender's threat model can't discount expensive attacks; the constraint is that an expensive one-off attack must not enable a cheap bypass. This is hard!