Frederico, acquiring a profound and proficient grasp of music theory is one thing, but becoming adept at innovation in music composition is something quite beyond music theory. Even so, and quite rightly, we do expect innovative composers to know music theory.
Perhaps we can regard music 'theory' as, albeit imperfectly, a collection of 'methodological and syntactical norms' used prior to and including this moment in history. Isn't it somewhat like studying a spoken language? As such, rarely if ever does such formal study afford the student any clues about where or how innovation is now possible, permissible or acceptable. Usage of the mother tongue of a culture is, I believe, the archetypal model of democracy, in that everyone participates and may - here and there, perhaps suddenly or over time, accidentally or deliberately, collectively or individually - bring about changes in usage of the language. That is to say, linguistic norms are not set in concrete.
And yet it appears there are many subtle but quite powerful 'anti-innovation measures' embodied in our participation of the culture, most especially in our usage of the mother tongue. After all, we don't want our understandings of each other via language to be seriously degraded or impaired by egregious departures from, or unwholesome perversions or corruptions of, our shared linguistic norms.
But by contrast to usage of our mother tongue, in the language of music there is considerable scope for not only novelties but also innovations. I distinguish novelty and innovation by considering that one's 'normality' is essentially altered by the latter, whereas the former may only perhaps 'colour' or otherwise alter our perspective of our normality in various non-essential ways. From even a cursory look through the list of composers in history deemed now to be "greats", it's hard to avoid the conclusion that innovatory prowess matters a great deal in our appraisals of composers; although of course several other factors, such as taste and style, also weigh hugely.
Innovation is an act of perfidy, whereas to abide by and support normality is fidelity. Innovators must of course be very careful to contain and limit their will to commit perfidious acts. There are some notorious examples of highly innovative composers and other artists who have allowed their will-to-perfidy to spill out into their social and moral life, with scandalous consequences (e.g. R.W.). Generally speaking, perfidy is potentially harmful to social and moral order and may, especially in certain ideologically rigid polities, in some cases be treated as criminally culpable. Little wonder that the art of innovation is not taught in academia - not that any art as such can be taught!
So where might this bring us vis-à-vis the contention here that composers with a background as orchestral musicians and/or conductors tend to be more adept and/or successful at composing? Given that innovation is a potent factor, I think it comes down to the norms of musical reality being far more real, alive, meaningful and powerful in the real presence of an orchestra, as compared to, for example, the case of an individual who has only ever tinkered with musical ideas on his DAW at home. To innovate necessarily includes, it seems to me, a profound appreciation of the power of current norms and normality, which is best acquired in real social situations.