I took all the music theory classes my university offered (while I was getting a different degree) and they were THE most fun and independently enjoyable classes I've had had, bar none. 7 years later, and I still think about all the days in class where we'd be doing something or talking about something and it was like a new door in my brain was opened.
So, with that said, I think if you can find a way to learn music theory enjoyably, please do that. I don't really know many of the different tools, guides, software ect. out there, but I know it exists. From what little I've researched, this software seems very useful: http://www.sheetmusicplus.com/title/Alf ... 0/19390197
It will probably take a lot of time to go through it all, but honestly IMO, IF one really wants to be a musician, they will
somewhat enjoy this learning process. And if you don't enjoy learning about it, then maybe music will just be a hobby instead of a passion or career. For example, even though you'll likely never, ever need to write figured bass, the lessons you'll learn from doing it will 100% carry over for the rest of your life when doing music stuff and writing bass lines, which you mentioned.
I mean, there's always a "throw everything at the wall and see what sticks" approach, but if you can sit down and write a main melody line, accompaniment and bass line BEFORE ever listening to how it will all sound together, and know that it will sound, at worst, just OK, then it saves you innumerable hours in the long run. This is where a knowledge of music theory can be useful as well.
And Ableton Live is soooooo powerful, and IMO session view is a musician's dream come true. Mozart, Bach, Vivaldi, etc. would've killed people to have these tools.
EDIT: Also, to add to the above, one thing I think a lot of people get caught up in in your cases is getting stuck in their own head. In other words, they DO have passion for music, but they can't get the idea from their brain onto paper (or computer screen). They have a melody they come up with in their head. Ok, fine. Then they hear a beat behind it. Also ok. Those are the two easiest things to transition from brain to computer. Some people have a knack for a catchy melody, which stems purely from their brain. Usually it's a set of one-note pitches, when you can eventually get down onto a keyboard or computer screen. And drums just kind of come from the head too. BUT, there just is nearly no way to hear a iii 7th chord transitioning into a V chord (ahhh, but in your head it has the bass note as the fifth, not the root note) resolving back into the root chord IN YOUR HEAD, and then taking the next step to actually get it into Ableton. There's almost literally no way, not without some music theory, or years of experience on the keyboard or another musical instrument.
What I'm trying to say is that learning music theory also is how you can take melody lines from your head, and turn them into living, breathing, moving musical passages. The point where you realize that you can come up with something in your head, then get it out onto paper or a computer screen is a good moment indeed. This is nearly impossible without music theory OR years of physical instrument experience.