Patryn, I notice your numbers do not account for power attack. Especially when discussing the 3.5 revision, that's a very significant flaw since optimally applied power attack can often add as much as 50% to a fighter's average damage/round.
Since the break-even point in the falchion/greatsword discussion is a function of the flat damage bonus, something that changes that bonus (like power attack--especially the 3.5 version) is an essential part of any valid comparison.
For instance, according to:
http://www.distanceeducationconsultants.com/ddcalc.php
A 3.0 Specialized 30 strength greatsword wielder with a +5 Keen, Improved Crit sword will deal:
217 points of damage/round against AC 10 with optimal power attack
171 points of damage/round against AC 20 with optimal power attack
127 points of damage/round against AC 30 with optimal power attack (though power attack only gives a +0.5 average damage boost at this level)
71 points of damage/round against AC 40 with optimal power attack (which is none)
http://www.distanceeducationconsult...d6&charge_mult=1&Ilove=Macy&button1=CALCULATE
Swap that 3.0 Greatsword for a 3.0 falchion and you get:
231.5 points of damage against AC 10 (PA: 20)
180 points of damage against AC 20 (PA: 8)
132.5 points of damage against AC 30 (PA 3 yields an average damage increase of 1.5)
72.5 points of damage against AC 40 (no PA)
http://www.distanceeducationconsult...d6&charge_mult=1&Ilove=Macy&button1=CALCULATE
Now, swapping to 3.5 and picking up Greater Weapon Focus and Specialization:
Greatsword:
AC 10: 285.5 (PA 20)
AC 20: 208.5 (PA 14)
AC 30: 135.5 (PA 5)
AC 40: 73 (no PA)
http://www.distanceeducationconsult...d6&charge_mult=1&Ilove=Macy&button1=CALCULATE
Falchion:
AC 10: 300.5 (PA 20)
AC 20: 218 (PA 14)
AC 30: 139.5 (PA 5)
AC 40: 73 (no PA)
http://www.distanceeducationconsult...d6&charge_mult=1&Ilove=Macy&button1=CALCULATE
If we want to see how 3.5 would look with crit stacking, the program seems to allow that (though it does cause errors):
Greatsword:
AC 10: 309.5 (PA 20)
AC 20: 226 (PA 14)
AC 30: 147 (PA 5)
AC 40: 78.5 (no PA)
http://www.distanceeducationconsult...d6&charge_mult=1&Ilove=Macy&button1=CALCULATE
Falchion:
AC 10: 335 (PA 20)
AC 20: 243 (PA 14)
AC 30: 155 (PA 5)
AC 40: 80.5 (no PA)
http://www.distanceeducationconsult...d6&charge_mult=1&Ilove=Macy&button1=CALCULATE
So, with that, it seems that 3.5 made a very noticable increase in the two-handed fighter's damage output per full attack--somewhere in the neighborhood of one extra hit per full attack. Allowing Keen and Imp Crit to stack would increase it even further.
I don't think that would be a real problem but it is worth noting that, in the 20th level comparison, the falchion is ahead at every point on the scale except against AC 40 without keen and improved crit stacking and at that point it breaks even.
The numbers would look different at lower levels (where +5 weapons, 30 strengths, and greater weapon specialization don't apply) and would also probably look different without power attack. They might look different even with suboptimal power attack numbers (though I suspect that they'd either be more or less equally suboptimal or that the greatsword would be hurt less by too little power attack and the falchion hurt less by too much power attack). The greatsword would also be slightly ahead against crit-immune opponents too. But it's certainly something to think about.