Rystil Arden said:
The problem with that analysis is that the Expertising character is unhittable to a character that was completely min/maxed to have the highest attack bonus, including choosing a Monster Manual race with +4 Strength. All the tank has to do is buy the standard defensive items and have 12 Dex (he doesn't even need the Tower Shield to be unhittable with the 2-for-1 Expertise at level 5). And even if he doesn't buy the magic items I assumed, he can still be unhittable *without a single magic item* to the +16 to hit orc! This is bad--seriously bad. It means that if you take one feat and don't even buy magic, just the full plate and tower shield, you're not going to get hit by any other character's normal attacks, period.
Let's revisit this analysis again because there are a few important things to consider:
1. This analysis is located at level 5--the most favorable point possible for the shield and combat expertise wielder. Locate the analysis at level 12, for instance, and the character will have a lot more trouble being unhittable. A 12th level fighter (since you are objecting to orcs, how about a standard array human fighter) might expect to have an 18 strength (20 with gauntlets of ogre power), a +1 sword, and greater weapon focus. So, he starts off at +20 to hit without any buffs (which he will most likely have--NPCs are only worth their CR if they are working together in a party that supports each other). In order to get an AC of 40, even with this rule, the character needs either a +3 tower shield and +3 fullplate or +4 heavy shield and +4 fullplate or some combination a ring of protection and an amulet of natural armor.
Of course, a 12th level fighter IS going to have those alternate tactics like disarming, sundering or grappling, so even then, it's not the best comparison. A cloud giant (CR 11) has an attack bonus of +22 (and Improved Bull Rush and Improved Overrun to put the fighter on his back or push him off a cliff). A CR 13 storm giant has +26 to hit (and Improved Sunder and Improved Bull Rush) as well as some nifty spell like abilities. A CR 12 displacer beast pack lord is +25 to hit with its tentacles. A CR 11 Dire wereboar hill giant is +29 to hit with his greatclub (and has Improved Bull Rush and Improved Sunder). A dire tiger is +20 to hit at only CR 8. A mature adult white dragon is also CR 12 and attacks at +27.
Did I cherry pick the monsters with good attack bonuses. Sure. But most of the other monsters have something else to do. A CR 11 Hezrou, for instance, couldn't hit the fighter but he doesn't need to. He has Chaos Hammer and Unholy Blight at will (along with a 3/day blasphemy that, if he has any allies, can be relied upon to destroy any 11th or 12th level party, but using blasphemy like that is cheating). A twelve headed hydra is CR 11 and only +17. But it has fast healing 22 and 12 attacks per round. So, the unhittable fighter can expect to get hit every couple rounds and, unless he hits two or three times per round himself, isn't going to inflict any lasting harm on the hydra. (A CR 12 eleven headed pyro or cryo hydra will just breathe on the fighter and toast him). Similarly, a Kolyarut is CR 12 but has enervation and vampiric touch at will and hold monster 1/day. A dread wraith is also in that CR range but makes incorporeal touch attacks. The point is that, by CR 12, any monster who is just a beatstick is going to have a higher attack bonus than the 12th level fighter can expect to get AND may have good options in addition to that. (Note that pretty much all the giants and the wereboar have Improved Sunder and the dragon has its (unimpressive--it's a white dragon) breath weapon).
The analysis has demonstrated that it can fairly easily render a character unhittable at level 5 (if he sacrifices most of his offense for it) but that doesn't last to the higher levels.
2. The character is only just barely unhittable with the magic items AND the tower shield AND 2 for 1 Combat Expertise while fighting defensively. The orc is +16 to attack. The other character is: AC 38 (10+9 armor +5 shield, +1 dex, +10 Combat Expertise, +2 fighting defensively). Without the tower shield, he's down to AC 36 maximum, and without the magic items or the tower shield (which you suggest is unhittable) he's down to AC 34 maximum which is hittable on an 18. And that's still fighting defensively along with the full combat expertise.
3. While the orc does represent the high attack point for a CR 5 NPC's, he does not represent the high point for creatures that a level 5 fighter can expect to face in combat (though I'll admit he is pretty close absent advanced or class leveled monsters, his attack bonus is better than any CR 5 in the Monster Manual). Fighter 5s have to be prepared to face a variety of creatures with CRs as high as 7 or 8. Dire bears anyone?
4. You are all vastly underestimating the importance of having an actual offense. The defensively oriented fighter has to be able to mount an effective offense if his defensive prowess is not simply to mean that he is the last PC to be killed. The usual tactic for monsters (or for PCs) when faced with an unhittable opponent who does not present a significant offensive threat (and when he's taking -8 or -10 to hit, the fighter won't qualify as a signficant offensive threat) is, absent any special manuevers (grapple, disarm, sunder, etc) to simply ignore him and go after the characters who are a threat. So the fighter doesn't take any damage. That does nothing to help the wizard, rogue or cleric, when the orc barbarian decides to take out his frustration on them. And without their support, the fighter is going to be in a world of hurt.
In the end, it may well be that the option is overpowered. But it's not as dramatically or as obviously overpowered as people seem to be suggesting. And a +2 bonus when shifting 2 points of attack to defense with Combat Expertise would probably end up fairly balanced. (As well as offering characters who don't get animated shields and two-handed weapons a benefit).