To say it yet one more way, any anus member who composes regularly probably is spending more time composing than reading these boards, in which case it's logical that their efforts would not be visible, and also logical when you are wondering why on such a music-obsessed message board are there very few who seem to write their own material.
I don't follow this at all. How is any of this logical conclusion from the suggestion that the composers amongst us spend more time composing than they do actively looking at the forums? The former takes a relatively greater amount of time, anyway.
In addition, speaking well and composing well are often not linked
What an absolute pile of rubbish. Consider, if you will, the fact that many of the greater composers from between the 17th and 19th centuries were court-musicians, who were retained in the company of well-educated nobles and, occasionally, royalty. These people would have been very "well-spoken", if that's what you mean. They would have been more than literate. In these instances, speaking well and composing well are emphatically linked. Perhaps you're referring to more modern composers? At this point, I can't think of many modern composers who I do not consider to be "well-spoken", at least to the standards of this board (given a few of the members here who are less than perfect in their English, for understandable and acceptable reasons).
The reason for this, I beg to propose, is that the nitty gritty of musical composition has very little to do with ideology, and "real" composers are often hilariously ignorant in areas other than musical poetics
Is a poet, then, primarily a shaper of words, and not a former of ideas? It would make a pretty shocking poet, a man who could merely describe his surroundings in flowery language (though most people would probably love it, being similarly vapid). The same is true of music. A great deal of composition has to do with ideology, principally the initial stages - what are you writing about? Why are you writing? What is it that is causing you to compose music?
These are the questions which must be answered before one can understand one's own processes of composition, one's own aim in composition. When this is not understood, it is possible to stumble upon greatness - Morbid Angel - and then lose it - Morbid Angel - but, understood, it is possible to focus on the goal and deliberately create works of genius - Burzum - even if it is possible to then lose the initial understanding under a wave of unnecessary complications - Burzum.
As far as compositional ability goes, this is often something that is developed with time, and rarely something that is innate to an individual (such as is called "genius"). Most great artists in European history created their most glorious triumphs in the latter years of their life, after having explored and experienced a vast portion of the field opened to them by the training gained in their youth, through whatever means. As ever, it is possible to stumble upon something great, as any man can crest a hill and happen to look down upon a mythical valley, yet unexplored by men, but it takes time, practice, and diligence to develop the skills and understanding necessary to be able to consciously mould one's goal into a musical form.