While I think I understand where your are coming from when you talk about the necessity of theoretical knowledge when it comes to composers, I have to disagree with your last statement from experience.
Yes there are full time musicians who do this and really don't know what they are doing. All they know is it sounds good. Also there are a lot of them who produce their stuff on their own, including programming arrangements for demos before something becomes a final product.
Is it really the composer who needs to have the knowledge or is it rather a social and work environmental expectation that they have to live up to?
I'm not saying theory doesn't serve a purpose. I just believe it's more on the prestige side than we are willing to admit.
We can agree to disagree!
I think, this is going around in circles. In short, by this logic, a food scientist, with no training or understanding of music can suddenly become a working composer, making real income.
It makes no sense to me whatsoever.
And if you read my sentence again, it does say - 'Absolutely Nothing'. To compose something, you need to know chords, harmony, rhythm, bass, structure, form, scales - something! Even if you did not go to college, you can learn these things either by figuring out, being around other musicians or learning from YouTube videos etc.
This is also theoretical knowledge. I do not mean, you need to be able to read a complicated piano concerto or a full orchestral score on demand. But, you do need something. And anything you pick up - no matter what the medium - that is theoretical knowledge.
Every professional will know 'some' theory. The level at which they know it, will depend on their background and the nature of music they compose.
A lot of it is also practical which can paralyze you.
Example:
You are at a scoring session. There is a conductor and a session producer. You need to communicate to the conductor that a certain passage needs to have shorter staccato playing. If you do not know where on the page it is, how the hell are you even going to communicate that?
If you do follow (at least your own music, like I can do), then you do have some understanding of theory and you can be in the room without costing the production a fortune to play 16 bars of music.
None of this is required to compose electronic music for example and there you do not need these skills but to say - you need to know nothing - not even scales, key, intervals - nothing is absurd.