Now if someone makes a specific claim like the fighter is a bodyguard because he does less damage over an encounter than a striker can, and yiu can show that the striker cant do more damage over an encounter, then yes you have a claim to truth there
The claim being made is that the fighter is a bodyguard rather than an "into the fray" combatant.
And the retort is that, while any given player may choose to play their fighter like that, there is
no mechanical support for playing a 4e fighter in that way (eg the fighter doesn't get many immediate actions which would support such an approach, unlike the paladin) and there is a huge mechanical incentive for the player of a fighter to get into the fray: namely, it's the only way (i) to mark, and (ii) to enforce your mark.
It is just like the arguments over whether the 3e fighter is sidelined by the wizard. It is going to depend on where the indidivuals thresholds are. Some people are going to see it that way, others are going to see it another. What mechanics achieve in terms of overall effect is a very subjective thing.
The only similarity I note between these two arguments is that one side - the 3E wizard is overpowered side, and the 4e fighter is not a bodyguard side - refers to the mechanics to support their claims, while the other side refers to mechanics-indepenent choices (like "we didn't make wands" or "we didn't scribe scrolls" or "my 4e fighter chose not to mark, because I thought the rulebook told me to play him as a bodyguard".)
There is a genuine difference of perspective here, but in my view it has very little to do with thresholds. It's to do with those who regard the mechanics as constitutive of the game, and those whose outlook is in some fundamental way that of freeforming, with social contract carrying a huge burden of both PC build and action resolution (but they still use the mechanics sometimes, for some things, although I'm not entirely clear what).
But in my view there can be no legitimate perspective on 4e's fighter mechanics that suggest that the 4e fighter is not mechanically well suited to being in the thick of melee. Between AC, hp, marking rules, and the almost complete absence of non-melee/close burst attacks, being in melee is the only way a fighter can bring any of his/her mechanical features and attributes to bear.
Saying that 4e's fighter mechanics encourage bodyguarding is as absurd as saying that AD&D's wizard mechanics encourage being a frontline melee combatant.