Gunblade is intended to be a hybrid item.

So why not make it scale better with hybrid builds over of AP builds?

55 AD 60 AP

UNIQUE – LIGHTNING BOLT: Instantly deals 1.25 Base AD + .3 bonus AD + .20 AP magic damage and slows the target champion's movement speed by 40% for 2 seconds (700 range) (40 second cooldown, shared with other Hextech items).

UNIQUE: Instantly heal for 15% of all damage dealt, including physical, magic, and true damage. This is 33% effective for area of effect damage. (This healing is reduced by 50% for ranged champs.)

What does this solve?

Lower active damage for AP builds and lower AP meaning not as good for mages.

Most of the champs who would classically considered item are melee who have a higher base AD than ranged mages.

All Healing done by ranged champs is reduced by 50% making it not a good sustain option for mages. This one might not need to happen if the other changes are effective enough.

Potential problems?

Juggernauts that don't have a name starting with M