In my case, given the musical circles I move in, I'll concede that if I'd learned to read, I might perhaps be doing more deps in function bands than I do.
A lucky escape, I reckon. Bit of course if I want to do more gigs like that, I'll put the effort in to learn.
Theory? Again, in my case, hardly anyone I work with bothers with the minutiae. We just write songs and parts, and play 'em. Some are theoretical geniuses, and I don't see them gaining any great advantage for what we do.
I guess if I wanted to do gigs like what Bilbo does, I wouldn't last 30 seconds.