Okay, let me rephrase the question then. What do you believe is wrong with a feat that boosts a defense that becomes useless at the higher levels, granting a bonus that essentially saves him 120k at said higher levels? What IS the problem with granting the Fighter what is essentially a low-level money-saver at the expense of damage?
You're not looking at the bigger picture. You're treating acting as though nothing else exists except Sword and Board sucking as an option, and this feat to "fix it."
6th level Fighter with Power Attack, Leap Attack and Shock Trooper, wields a +1 Greatsword, wears Full Plate, and has 20 str. On a charge, if he power attacks for 6 (which he does), he deals 2d6+7+24 damage, avg 39. He has 20 AC (14 after a charge) and 11 Touch. He has a +12 to hit, hitting the S&B guy 30% of the time, avg resulting damage of 13.
6th level Fighter with Shield Spec, Shield Ward, and Shield Guard, wields a Longsword, wears Full Plate, and has 20 str. Every hit he deals 1d8+5 damage, avg 9.5. He has 27 AC and 18 Touch. He has a +12 to hit, hitting the Charger 65% of the time, or 95% of the time after the Charger charges, avg resulting damage of 6~9.
Now, these two builds seem relatively balanced against each other, however, the first build needs Shock Trooper to deal that much damage. It needs all three feats to do its thing. The second build doesn't need Shield Guard. That feat actually gives him new, unique capability that helps his allies. I come again to the point I made earlier, where if somehow the benefits of Shield Specialization were split into two feats (probably using a different mechanic than just adding the Shield bonus straight up), I would have far less objection to the result.
Something like these?
Shield SpecializationPrerequisites: Shield Proficiency
Benefit: You gain an additional +1 Shield bonus to AC while wielding any shield.
Special: For every five Fighter levels you possess the bonus granted from this feat increases by 1.
Grand BulwarkPrerequisites: Shield Specialization, Base Attack +6
Benefit: This feat grants you two special combat options, as follows;
Impenetrable Glare - As a swift action you can double your Shield bonus to AC against a single foe for 1 turn.
Defender's Aegis - As long as you wield a shield, as a swift action, you can deny line of effect to a single adjacent ally for 1 turn.