Hmm. The paragon paths do seem to help. I can't really comment on how the game plays at paragon level because I haven't actually . . . played it much. My first 4E campaign still has all the characters at level 8, so I don't know how the classes compare as tanks once all the paragon paths, new powers, feats, items, etc. are taken into account. Still, those paragon path fixes strike me as too little, too late.
I can comment from experience on the heroic level, and I know that there, fighters are better tanks. Their main edges seem to come from Combat Superiority, their ability to mark many foes at once, and the fact that even shifting monsters can't get away cleanly. Well, and their mark damage is simply better. Paladins get, like, 7 or 8 for damage. Fighters get 1[W] + STR + Weapon Enhancement + Bonus for it being a Tuesday + any 'on a hit, you're hosed' item/weapon powers the fighter feels like activating. (Mind you, monsters avoiding damage is a losing game for them, but still. It's a difference.) Fighters even get powers like 'Come and Get It' which pretty much force a lot of monsters to go after them. Paladins don't get anything like that, that I know of.
I'm not saying that's a problem from a balance perspective or that fighters are better as defenders (though I think they are)--I'm simply noting that the difference in effectiveness as tanks is counterintuitive. From an RP perspective, I would expect all of the fighter's abilities to push people around and generally micromanage the battle line. What I wouldn't expect is that monsters were always hitting the fighter and ignoring the paladin.
I mean, paladins are supposed to be martyrs, right? "No, hit me!" is supposed to be their battle cry.
The insight I gained from this conversation is that mark effectiveness translates, not to defender effectiveness, but to tank effectiveness. If I wanted to make paladins all tankish and super-martyry, all I have to do is give them a better mark.
I mean, a much better mark.
Something like this:
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Single Combat Dare
Encounter - Divine - Implement - Charm; Paladin Attack 7
Minor action; Ranged 5
Target: One or more Creatures
Attack: Charisma vs. Will
Hit: Until the end of the encounter or the incapacitation of either the targets or the paladin, both parties are Locked In Combat.
Locked in Combat: The Locked in Combat condition applies to a group of creatures, the combatants. While Locked in Combat, a combatant who attacks any other target is Dazed (save ends) at the start of his next turn.
Furthermore, outside interference invites divine retribution; anyone who attacks either combatant and deals damage or inflicts a condition causes himself and the other combatants (any he did not affect) to automatically take identical damage and suffer an identical effect.
You cannot challenge someone to single combat who is already participating in one.
The Locked in Combat condition ends when either party is incapacitated, or when side has completely escaped--defined as being out of line of sight for five minutes.
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That would be a paladin's mark with teeth.