Is two-weapon fighting only as a full-round action balanced versus fighting with a two-handed weapon?

Question

One of the players in a Pathfinder game in which I am playing is arguing that characters should be able to get the additional attack for fighting with two weapons when attacking as a standard action, instead of a full-round action which is normally required to get additional attacks.

He argues that a character that dual wields a longsword and a shortsword with Two-Weapon Fighting and Improved Two-Weapon Fighting is a decent amount worse than a character that wields a greatsword and has Power Attack and Vital Strike.

Full Argument:

Two weapon Joe
Point buy (ultimate min max 15 point buy)
Lvl 11 (so he can get most of the twf feat chain)
15 dex +2 race +2 levels = 19 (twf req)
15 str
Feats TWF, Improved TWF, Greater TWF (and some others but these are the important)

Weapons +2 Flaming Frost Longsword, +2 flaming Frost short sword (note this is almost all of the chars WBL)

BAB +11 +2 str +2 weapon = +15, so Standard action TWF +13 (-2 twf)/+13 (-2 twf)/+8 (additional -5 ImpTWF)/+3 (additional -10 Great TWF)

Assuming all hit (not very likely) dmg 1d8+2 str +2 weapon +1d6 fire, 1d6 frost, 1d6+1 str (+same modifiers) x3

Average dmg 4.5+10.5 +13 physical frost +14(4x3.5) +14(4x3.5) fire. Total:56 combined dmg/round

Two handed bob
Lvl 11
16 str +2 race +2 level: total 20
and still has 5 points to spread around to other stats
Feats: power attack, Vital stike, Improved Vital stike
Weapon +2 Flaming frost Greatsword (still has tons of wealth left over for other stuff)
BAB: 11+5str+2weapon= +18 to hit. Standard attack vital Strike power attack: +15 (-3 pow attack).
Damage: 6d6+7 str +9 power attack +2 weapon +1d6 frost +1d6 fire
Average: 39 physical +3.5 fire +3.5 frost Total = 46 combined dmg

Analysis:
Total Average twf with standard: 56 combined
Total Average two weapon: 46 dmg.

Adding dr 5 and elemental resistance (not that uncommon at level 11)
TWF now deals: 8 damage
Two handed deals: 33 still and he has 32000gp extra to boost his combat effectiveness

I'm personally of the opinion that this restriction is in the game for some reason, especially since it survived the transition from 3.5 to Pathfinder, but I can't really wrap my head around the reason.

Ignoring the potential to slow down the game with additional attacks and looking strictly at balance, is two-weapon fighting only as a full-round action instead of as part as a standard attack action really balanced versus fighting with a two-handed weapon?

To clarify after reading AceCalhoon post. I was only calculating adding my house rule to allow the standard action additional TWF attacks. to allow a TWF to have mobility and keep up with damage roughly to a Two handed fighter. So that is why I didn't include the itterative attacks from BAB

Answer 1

In 3.5 "there's a feat for that" you could grand-father that in... Or give your players time to re-build their character with an Archetype from the Advanced Players Guide. Two-Weapon Warrior is a crazy archetype that would give him the following ability at 9th level.

Doublestrike (Ex): At 9th level, a two-weapon warrior may, as a standard action, make one attack with both his primary and secondary weapons. The penalties for attacking with two weapons apply normally. This ability replaces weapon training 2.

If you don't have access to the APG, or any of the other books detailing the various archetypes you can check them out on the SRD. I know that in general my DM hates them, or he did before i showed him how much more fun and flavor they can provide players. Sometimes they can turn you into a "one trick pony" but otherwise they just take what you want to be good at, and make you better at it!

The 3.5 Feat from Complete Adventurer was Dual Strike:

Dual Strike

You are an expert skirmisher skilled at fighting with two weapons. Your extensive training with two weapons allows you to attack with both while moving through a chaotic combat or fighting a running battle.

Prerequisites: Improved Two-Weapon Fighting, Two-Weapon Fighting.

Benefit: As a standard action, you can make a melee attack with your primary weapon and your off-hand weapon. Both attacks use the same attack roll to determine success, using the worse of the two weapons’ attack modifiers. If you are using a one-handed or light weapon in your primary hand and a light weapon in your off hand, you take a –4 penalty on this attack roll; otherwise you take a –10 penalty.

Each weapon deals its normal damage. Damage reduction and other resistances apply separately against each weapon attack.

Special: When you make this attack, you apply precision-based damage (such as from sneak attack) only once. If you score a critical hit, only the weapon in your primary hand deals extra critical hit damage; your offhand weapon deals regular damage.

A fighter may select Dual Strike as one of his fighter bonus feats.

This feat has some interesting flavor, but it balances really well too: you only use one attack roll for your standard action, and at a decent penalty too. That giant you just carved an X into wouldn't be too happy.

Answer 2

Two-weapon fighting has a number of perks over two-handed fighting, although I'm not saying the math comes out entirely equally. Now I admit many of these, require a full attack to take advantage of, but they are useful in discussion about the two fighting styles.

1. To start feats such as Greater Two-Weapon Fighting or Improved Two-Weapon Fighting give you way more attacks than an equivalent two-handed fighter.
2. Damage dispersal - with two attacks as a full attack, you can attack twice as many creatures. A greatsword is great against a dragon, but if you need to mow through a field of goblins more swings will help better than massive damage.
3. Damage per attack abilities will get multiplied - the more hits you get, the more times you can apply sneak attack bonuses, or flaming weapon damage, bonus strength damage or even enchantment bonus damage. Admittedly, it will be a little more expensive to enchant two weapons.
4. Disarm resistant - you are not completely neutered if you get disarmed.

Answer 3

Yes, it's balanced.

The thing is, whichever configuration you take, you can work on infinitely twinking it out. Two-weapon fighting is better when you want many more attacks. Being a rogue with sneak attack is the number one example of this. Or if you bleed per attack (like with Bloody Assault). Or use poison. Or use the various critical effects from the critical feats. Or want to use some of those attacks for trip/disarm/sunder attacks.

Sure, two-handed is better when something has DR. Per-attack damage plusses and minuses and additional conditions affect a two-weapon fighter much more than a two-handed fighter.

A straight fighter will do more dps in an abstract sense with a two-handed weapon than two-weapon fighting, if all he does is straightforward hitting without any other interesting feats. But if you change the TWF rules, your player is just going to turn around and layer the other TWF twinks on top and suddenly it's the more powerful thing, and you have to start worrying about your two-hander player... Because he who inflicts the most damage wins the game, apparently.

Also, there's a difference between optimization and real play. Real adventurers find gear, they don't "have 32000 to spend on it." I've played and GMed a lot of Pathfinder, and players have run and enjoyed two-weapon characters as much as two-hander characters. (Sword and board, however, sucks.)