Hey Bro,
Being a teacher , if I had to just GUESS from what youve stated thus far I would say # 1 ,he's been spoon feed those 8 min. tunes, either demostratively OR Tab. IMO ,when you learn something visually, you cheat the EAR out of developing the aural muscle memory needed for improvising and/ or just even picking up where "Mary had a little lamb" is in the Key of Eb ..He likely has trouble with easier tunes becuase he's probably using a different method to internalize them, like maybe by ear.
Trouble is, his LH is NOT recieving any muscle memory info from the brain. Thats where Ear training comes in.I have a student that is like that.
He'll play some wicked piece that he got TAB from the net , BUT has trouble hearing the notes available to him in a blues or pentatonic /diatonic scale.OR even a chord formation..Yeah , We heard our Own GA speak of going back and gettin the rhythm structures where melodic and improvise breaks/solos come from.Once those keys are internalized, the skys the limit...NOW, you would think armed with all this knowledge Iwould be a better gtr player..

..Well, then there comes this thing called "technique"which I LACK..(I dont practice either)...Yeah ,Andragon , elaborate alittle more if ya can..I like talkin this kinda stuff..
John