I'm not always the best with rules, but aren't there a few problems with the example demise of the paladin?
jackston2 said:
... when Bar-Lguras swoop down and start wrestling the adventurers. The Mage dimension doors away, and the rogue escape artists out of their grasp...
I would think that the rogue's ability to escape artist out would be at least moderately close to the paladin's ability to out-grapple a bar-lgura. The rogue's escape artist check is probably only 3-4 points higher than the paladin's grapple check, assuming equal level and max skill points from the rogue.
jackston2 said:
...but the NPC Paladin is teleported 2000 ft in the sky (will save...)
Assuming you mean that the Bar-lgura teleported with the paladin, there is some non-standard stuff going on.

The Bar-lgura can only teleport itself and up to 50 lbs of objects--it can't carry passengers.

Teleport (the spell-basis for the Bar-lgura's teleprt ability) only allows the transport of willing targets. I'd be reasonably certain that the paladin was not willing. The Teleport spell mentions a saving throw for items (that the 'porter is trying to "steal" with the teleport), not for unwilling passengers.

Creatures transported by teleportation (like all conjuration effects) must arrive in a location capable of supporting it. No instant-falling.
jackston2 said:
...Except for diplomacy. Since the Paladin witnessed his entire regiment get slaughtered by Strahd, he tried to use diplomacy to make a pact with the Bar-Lgura (In game reason: The Paladin decides that losing his status is worth being able to cleanse the land of evil/ Out of game reason: The group would suffer TPK without a defender).
I would be hard-pressed to think of any paladin that would so easily bargain away their status, but then, the paladin should never have been put into that position.
jackston2 said:
Anyway, the Paladin fails his diplomacy and slams into the ground taking 1,990d6 damage
(Someone already caught this, but the typo they made bears correcting) Falling damage is capped at 20d6. That is somewhat more survivable.
jackston2 said:
and is sent straight to Hell where he is tortured for all eternity for bargaining with Demons.
I hope you didn't describe this, as the players should never have known this; it seems like either an empty point or hyperbole, to me.
(Editted to add) On the more general topic, I find defenders quite entertaining, and the 4e material definitely makes it seem more viable than previous editions. I might recommend that you suspend the addition of NPC defenders, though. I think you are reinforcing the negative opinions of the party by including them, and they are not learning that the role is, if not necessary, at least extremely useful. I would also recommend against changing the encounters. Certain encounters may be more difficult, but that is often true for non-standard parties. It's the nature of the tactical part of the game.