I feel your pain. I think they're harder because play them out of the chord form but in a flat picked song, you can sort of abandon the chord positions and just play the melody. Also, with a flat picked song like Old Joe Clark, you can just plant your pinky and keep your right hand in position throughout the song - but I have trouble if I have to strum chords and then get my hand back into position - I miss alot of melody notes in between the chords. Finally, the flat picked songs are all usually the same notes (quarter notes, eighth notes or whatever) but the chord songs seem to mix up the up and get complicated to keep timing in the leads. I've been working on Loch Lomand and have trouble with this song for that reason.