I can relate, and I'll share one of my biggest mistakes so you can avoid making it: trying to do everything, and ending up doing very little because focusing on "everything", isn't focusing at all. Not just in guitar playing, but in life, without clear goals and a lazer sharp focus, it is very difficult to make serious progress. We have to "tame the monkey mind" as they say in zen. What you exclude from your limited practice time is almost more important than what you include. Jerry Garcia used to say that a musician is largely defined by her/his limitations. You have to get creative to find ways to express yourself within those at any given moment in time. You have limited practice time, so you probably won't master blues, classical, folk, jazz, Indian ragas, bluegrass, etc, but you might make exciting progress if you narrow your focus a bit.
I wouldn't get too hung up on how you define greatness (that goes double for how anyone else does). Unlike being a great mechanic or lab technician, this is art. There is no single standard, or prescribed course of study.
Having said that, I hear your frustration, and it seems you might benefit from taking a composition class, or at least study it on your own, as indicated by your wanting to understand why songs are structured as they are. (Keep in mind a lot of songwriters are pretty intuitive, simply experimenting until they find a chord sequence, and/or melody that "sounds cool").
You might consider following Tony Robbins' advice to find somebody who produces the kind of results you want to produce; learn everything you can about how they did it; their knowledge, physical techniques, mindset, etc; everything; really get inside their brain. Then model it. A caveat though; ultimately you want to use the inspiration, techniques, songs, etc, of others as a starting point, because the one thing that you can say about all the greats is that they sound like themselves.
Hope that's helpful and not too long and pedantic. Good luck, and let me add one more, perhaps most important piece of advice: stay in touch with your joy, enthusiasm, excitement, love of music, and your instrument. Celebrate that you've come as far as you have! It's fine to get bored with your playing; that's part of what drives progress. But try not to put yourself down; you aren't a "poser"; you're a person who loves to play and does it at a level that's good enough to entertain some people; that's a gift that you give to the world every time you pick up your axe.