There's an Alan Belkin letter that addresses your specific concerns posted somewhere on this site.
To paraphrase, being a composer is not the same thing as building a career as a composer, whether for recognition, money, or both. In fact, the latter will demand time from the former, all things being equal, as well as often imposing more artistic limitations than would otherwise exist. So there is a definite upside to composing in relative isolation.
I think it was Aaron Copland who wrote that many composers do what they do because they are basically compelled to do so. And in a lot of ways, the existence of tools like GPO just make that proposition all the sweeter.
And finally, in moments of doubt, a note from Martha Graham:
"There is a vitality, a life force, an energy, a quickening that is translated through you into action, and because there is only one of you in all of time, this expression is unique. And if you block it, it will never exist through any other medium and it will be lost. The world will not have it. It is not your business to determine how good it is nor how valuable nor how it compares with other expressions. It is your business to keep it yours clearly and directly, to keep the channel open. You do not even have to believe in yourself or your work. You have to keep yourself open and aware to the urges that motivate you. Keep the channel open."Regards,