No, I linked to the source and quoted the relevant point. I believe all three sentences in the paragraph are cumulative but independent points that explicitly do not preclude each other. Any item of itself is sufficient to preclude the calling of the API.

By default, the page is eligible if the API is used in the page, but the website owner can opt out of that using the header setting, and the user agent should offer a permission setting to disallow sites for inclusion by users. The second and third sentences would not exist or make any sense if the first sentence precluded them.

The full text of the paragraph is:

''' 7. Privacy considerations 7.1. Permission 7.1.1. Eligibility for a page to be included in the interest cohort computation

By default, a page is eligible for the interest cohort computation if the interestCohort() API is used in the page.

The page can opt itself out of the interest cohort computation through the "interest-cohort" policy-controlled feature. [PERMISSIONS-POLICY]

The user agent should offer a dedicated permission setting for the user to disallow sites from being included for interest cohort calculations. '''

There are multiple reasons why the API could be included in the page, but a website owner choose to opt out using the header, or a user disallow it. I agree it is confusingly phrased but it is a draft, and the meaning seems clear to me.

It sounds like you're reading in an "only" that isn't in the text.

As written that quoted part gives a reason for inclusion, but not a requirement (ie the condition might be 'sufficient but not necessary').

High percentages of pages are using GA, and it would be trivial for GA to start calling document.interestCohort() at an indeterminate point in the future. Better safe than sorry.

It's safe to assume that all Google services will require FLoC by default (Analytics, Firebase, etc). Time to switch.