1- AC: With a shield defenders are probably going to have equal or maybe one point on a striker, without a shield it's pretty easy for a striker to have a better AC.
A defender with the highest AC in the party is not as good at his job as he could be. If he's too hard to hit the enemies will target the squishier party members instead. They'll have -2 to hit when marked, but it won't matter because they'll still be as likely to hit.
2- Marking: So you can get the attention of one guy, well in your average 4E combat there's a lot more than one guy, and yes there are some encounters and daily powers that allow marking of more than one but their core class ability let's them get the attention of one dude, and it has to basically be a dude that they're adjacent to anyway. Now I don't have any hard math here, but in my experience the defenders do most of their "locking down" in the same way everyone else does. Threating Opportunity Attacks and providing occasional cover vs. ranged attacks.
Fighter lock down comes from his ability to keep foes from moving away from him. The occassional ability to mark multiple people is nice, as it gives the rest of the party a pseudo-+2 to defenses, but it's the ability to get up to foes and keep them from moving away that helps. He doesn't just threaten OAs, his OAs stop them in their tracks.
Paladins' lock down comes from their free damage if the enemy attacks anyone but them. It's not as good at defending as the fighter's abilities, but paladins make up for it with increased healing ability for others.
To put it another way I've seen only a few instances where marking really changed who a monster would have attacked and even fewer where having the monster attack the defender as opposed to someone else really changed the course of a combat.
Have you never seen a monster miss by one or two because of the -2 penalty for not attacking the one that marked them? Have they never taken any paladin challenge or the fighter's interrupt attack? An enemy dropping earlier and missing on attacks is a big difference in how many surges are spent and who might drop.
3- Reflex, Fortitude and Will Defense: I'm sure there's some math to be done here, but just eyeballing I don't see any reason either from the numbers or from play experience to see any reason why the "Defenders" are any better at "defense" in this area then any of the other roles.
They're not supposed to have higher defenses, they're supposed to defend others.
4- Hit Points: Here defenders have a clear advantage, but how much of an advantage is it really? I'd say just based on eyeballing it that it allows them to take one, maybe two more hits than a leader or a striker.
Two hits is a lot.
In my play experience the defender gets the lions share of the healing and still goes down more than any other character.
I'm confused. The defender is taking the most damage, but he's not defending the rest of the party?
Much Better? Just to take the paladin as an example once he gets through putting his high stat's and stat bonuses into str, wis and cha he'll be lucky to have a higher con than the rogue or ranger.
Why is the paladin trying to be good at everything? If he picks a single aspect of his class to focus on and just makes sure he's decent at the other, he should be fine. Each class (except Wizard) has at least two primary foci. Any character trying to do both well is going to suffer elsewhere.
So let's say they both end up with a con of 12, that means at 30 level, where the hit point difference is the max, the Paladin will have 207 to the ranger/rogue's 174. That doesn't seem "much better" to me. As I said that's one hit.
A level 30 soldier (advanced Efreet, since all level 30s are solos) does an average of 22 damage per strike. Not including his higher healing surges, that's 2 more attacks the fighter can take. When you factor in his 200 hit point advantage from having larger and more healing surges, the difference seems pretty huge (11 more attacks per day he can take, assuming all other factors are equal, which they won't be because fighters can easily get regeneration for an entire encounter or heal themselves without spending a surge, or that Cha focused paladin can be adding his Charisma Mod twice every time he lays hands on himself.
Yeah they have a few more healing surges, but particularly when you're talking about the fighter, they don't have anyway to really use them.
Short rest
Comeback Strike (daily on hit)
Iron Warrior (daily minor action that gives more hit points and a save)
Indomitable Strength (daily Iron Vanguard power)
It's not a lot, but it's more than most get. Multiclassing Warlord or Cleric is a good bet for fighter's, and since they take a lot more damage than others, they spend more surges via the rest of the party;s healing powers as well.
It's much more common to run out of ways to use them...
Short rests.
So the ranger is the equal of the two-handed weapon fighter, that doesn't necessary rebut my point (I really think defenders should always have better AC at least by a point or 2). Also if you assume that that ranger started with an 18 rather than a 17 (obviously not unheard of) the it would be 34 to 33 and we're back in a situation where the striker has a better AC than the Fighter without a shield.
If your fighter is worried about AC, he should use a shield. +3 to AC and Reflexes (+2 before Shield Spec) will put him even or ahead. If he wants to focus on damage, he has to accept the downside of that decision.
Better Healing surges for defenders? Are you saying that because they have more HP? They're only going to be better by 1 or 2 points once you divide everything by 4....
Sure, at 1st level. At 30th (by your own numbers) it's a difference of 8. And that's again assuming the fighter is dumping Con, which given the regeneration stances, is a pretty bad idea.