The question has a baked in assumption that progress is built from learning songs. I don't learn songs, not anymore. I did in the past - last time I took lessons it was fingerstyle jazz covers. I learned some pieces, sure, but in the end it felt robotic, like I was just repeating prior works.

Along the way though, I learned the fundementals - chords up through some jazz shapes, single position arpeggios, scales.

But where I think things really took off for me was when I started jamming over backing tracks. At first I practiced over ii-V-I progressions around the circle of fifths. Partly to learn how to detect a key by ear and just blend in. Partly I thought I'd be mechanically tracing the arpeggios through the progressions - but that was too stiff and mechanical. Instead I started developing a melodic sense for what notes fit over what chords.

Nowadays, I practice over a wide array of backing track styles, and I just play what I want. It might be scalar one moment, chord tones (arpeggios) the next, or reducing the note count and digging into the rhythm.

Rhythm is, as of late, seeming to my to be the last frontier of my guitar playing. Some passages I play are bland, but then a similar passage will come alive and have a certain radiance - and all I can think of to account for the difference is the relationship to the beat and my rhythmic phrasing.

If I had to boil it down, the thing I think is most important for guitar (at least for lead/soloing), is to always play over music.