A spell that creates a creature, an object and an ongoing effect is dispellable by targeting any one of those, even if all of those are the same thing. A spell that does multiple things simply has multiple vectors for dispel magic.
Shadow blade has target "self". So casting dispel magic on a creature with shadow blade should end it. It's not controversial at all that the shadow blade should end.
In fact it says any spell on the target ends. So if you target a creature with multiple ongoing effects it should dispel all of them. If you have mage armor, disguise self, mirror image and shadow blade and someone casts dispel magic on you, all 4 of those spells end.
Furthermore, if someone casts Conjure Animals and summon 8 wolves, casting dispel magic on one wolf should dispel all of them, since it ends the spell, not the spell effect.