What your argument is missing is that I'll ship security issues that would have been caught otherwise.

You're assuming that these won't matter because attackers might not have better models than I do, but that doesn't make sense. The assumption that attackers can't find the issues because I didn't find them at release is wrong. Even if they never get better models (which they will), current models might find flaws I missed, and they also have other means of finding flaws in my software.

The best defense is to make software as secure as possible regardless of assumed attacker capabilities at the point of release.

It’s highly likely that everyone has software or firmware made by Chinese engineer running in their house.

These defenders aren’t supposed to have access to the “defender models”.