Someone should tell the melee druid that he's a defender. I doubt he knows this.
He usually figures it out after he gets knocked unconcious a few times.

More specifically, if your druid is getitng enemies to attack him rather than not be able to attack at all (or at tack the defender) he's playing defender--and he isn't very good at it. The sentinel can manage it better, despite being a leader, because he can take controller powers and use his pet as a pseudo-controller (if, yes, it doesn't die. But then, a defender can die too).
I'd prefer a defender at ranged who gets enemies to attack him at ranged, or who forces melee guys to come get him. But he has few melee offense/defenses. So the idea is to 1) Draw enemy ranged fire, 2) draw enemy melee guys.
The problem is that this is either awful or problematic. A defender's assets consist largely of stickiness, threat, and defenses. It's possible for them to do without threat (if the stickiness and defenses are good enough), and even sometimes without stickiness if the threat is strong enough to act as pseudo-stickiness, but the defenses--and using them actively, is non-optional.
The problem with a ranged defender who largely acts on ranged opponents is that melee opponents are far more common. So it's a trap.
The problem with a ranged defender who can keep out of range and force melee opponents to close is that it's largley unbalanced; you're not taking hits, so you're not really using your defenses as one of your assets in this situation. So if it's too weak to work, it's just weak; if it's weak enough to be effective, you're being a controller/striker with defenses like a defender, and that's just too much.
Thus, the idea of a pet defender.
Regarding a pet defender, I think it would be -easy- to make one a Shaman subclass. Remember, the shaman doesn't need defender defenses/HP; only the pet needs this. The defender shaman can probably get away with defender defenses and mage (ok, probably cleric) HP, as if you keep the existing "when the spirit dies, you take 5+1/2 level" mechanic, you're effectively taking half damage (or less) and getting double healing. Drop the leader healing for better defenses (or at least better defenses for the spirit) and a way to let the spirit mark enemies and you're nearly good to go (you probably a defender spirit -not- to vanish when a hit gets through its resistance, as then it stops defending, and that's kinda bad).
Also, for a ranger style pet defender, I'm not seeing the problem with "the pet can die". Of course the pet can die. If it does, the party defender is dead! Don't let that happen! You know, the beastmaster ranger in a party can die too; the player can keep playing the beast until it also dies or the ranger's raised, but, well, the party's down a ranger. The fact that the player can play a far weaker verison of their character once the "business" side of the pair is dispatched is an a feature of the build--not a sign that the ranger is not a true striker.