Agreed that learning intervals and chord tone degrees is important. It is indeed supported by having familiarity with the underlying notes since they comprise the chords and scales.

Learning the fretboard helps players to find chords and chord inversions further up the neck. For example, the player knows they can move the E shape to the barre A position, which preserves all of the interval relationships from a new root.

Knowing the fretboard notes is a bit like playing in daylight rather than campfire darkness.