>Plus, it should be super easy for you to fix this - all you have to do is remove the check for "subform" and drop support for that field in your API.
It might not be that easy, because there might be a bunch of users currently depending on the current behavior, and as soon as a real ReCAPTCHA token is required, they will break. They might need to introduce a 3rd ReCAPTCHA option. So they would have 3 options "ReCAPTCHA off", "ReCAPTCHA legacy weak", and "ReCAPTCHA on".
It might not be that easy, because there might be a bunch of users currently depending on the current behavior, and as soon as a real ReCAPTCHA token is required, they will break. They might need to introduce a 3rd ReCAPTCHA option. So they would have 3 options "ReCAPTCHA off", "ReCAPTCHA legacy weak", and "ReCAPTCHA on".