ILR
This site has information about the Foreign Service Institute's definitions of fluency for students studying foreign languages. It might have some relevance here, as some have said that for deaf children, particularly, English or any other spoken language is a "foreign" language to them, as opposed to sign-language.
The scale goes from 0 (no fluency or ability to say anything beyond a few words in the target language) up to 5 (the fluency of a native, well-educated speaker). There are other sections for evaluating reading and writing which use the same scale.
Note that you can be considered quite fluent (4+ level) and still have an accent. That might cover some who speak with a "deaf accent."
For a level 5 speaker, however: "Pronunciation is typically consistent with that of well-educated native speakers of a non-stigmatized dialect."
Professional Foreign Service officers typically must achieve 3/3 (speaking/reading) fluency levels in the target language (the language of the country to which they are assigned), and they are strongly encouraged to keep improving their language fluency while at post.
So perhaps some here who are arguing that HoH and some deaf (especially late-deafened) individuals are "fluent," they might be accepting a level of fluency that might be graded anything from 3 up to a 5. (A 3 can converse well, but might have some vocabulary or pronounciation deficits.) But those who are saying "No, that's not true, no deaf or HoH individual can really be fluent in English or any spoken language" are thinking only of the highest level, the "functionally native proficiency," and believe that no HoH/deaf person reaches that level.
Here's the page for writing:
ILR
Grammar and spelling errors would prevent someone from being classified at Level 5, "functionally native proficiency." Even a Level 4 should be "able to write the language precisely and accurately..."
For reading comprehension, the breakdowns are similar.
ILR
FS Officers get a two-part score, with the first number being for spoken language and the second one for reading. It is very common to have a higher number for reading than for speaking. For instance, I have a 3+/4 in Spanish - my reading is half a level better than my speaking.
Maybe some of the deaf educators here could hazard a guess as to what might be typical scores for their students. Perhaps their scores also might very commonly be better in reading than in speaking; that wouldn't be surprising at all. You could probably evaluate ASL usage the same way; a well-educated native signer being a "5," and lesser abilities at producing and comprehending would be at the lower levels.