Mike:
It seems to me that the great works you describe and other like examples of true compositional greatness were, in most cases, created over extended periods of time. Many of these works took months and even years to write and orchestrate. Even so, they were often revised extensively by their composers.
Certainly, Bach, Haydn, Mozart and many composers of the 16th and 17th centuries worked under tremendous time pressure and had to produce a lot of work in a short period. However, most of the composers of those eras produced only pedestrian work at best. Only the few true geniuses were able to create great works under those conditions. From the 18th century onward, it seems to me that great compositions were mostly the result of a combination of talent, tremendous education and a lot of time.
Of course, it is possible that I am wrong about this but, I don't know how it is possible to create extended works at the highest possible level with a deadline of the kinds most of us work under. This seems true whether you are in Film, Television, Games or in my world of the Theatre. For myself, I completely empathize with your statement, "I hear my own work and I see a galaxy-sized gulf between my work and the work I truly am inspired by." I know for sure that I am not good enough to do great work quickly. Of course, I don't know whether I can produce great work at all. I do know that the only chance for that to ever happen is if I find a way to take more time than I do now.
Be Well,
Poppa