Anyway, time to bring calculations into the argument. There are damage formulas on GameFAQs for this, actually. Although the raw power differs greatly, the class of the weapon reduces its power accordingly. Sword and Shield is reduced by a factor of 1.4 while the Greatsword is reduced by a factor of 4.8.
Now, I have a hypothetical situation below. The weapons are high rank, although the monster is low rank (The power differentials shouldn't matter too much unless you're making an argument that the SnS is worthless based on its non-elemental beginner weapons).
A good GS user should have Critical Draw. Likewise, a good SnS user should have a decent elemental against that monster.
Monster: paralyzed low-rank Barioth
Hitzone: Head
GS: Diablos Hornsword
SnS: Blazing Falchion
Barioth weakness on head 55%. Elemental weakness 35%.
Equation: [Attack power x type x sharpness x [crit draw] x Hitzone] / Class
Crit. Draw is only available for GS.
Elemental damage: [Element x sharpness x hitzone] / 10
Only available for SnS. GS has such poor elemental damage, which is unaffected by Crit. Draw,
that it's better to have a higher raw damage.
Greatsword:
1008 x 1.10 x 1.2 x 1.5 x .55 x 1.05 / 4.8 = 240.12 - Crit. Draw Lvl 3 Charge
Sword and Shield:
238 x .16 x 1.2 x .55 x 1.06 / 1.4 = 19.03 - Jumping Slash
440 x 1.0625 x .35 / 10 = 16.3625
238 x .13 x 1.2 x .55 x 1.06 / 1.4 = 15.46 - Regular combo 1
440 x 1.0625 x .35 / 10 = 16.3625
238 x .11 x 1.2 x .55 x 1.06 / 1.4 = 13.08 - Regular combo 2
440 x 1.0625 x .35 / 10 = 16.3625
238 x .08 x 1.2 x .55 / 1.4 = 8.98 - SnS combo 1
No elemental damage (shield)
238 x .12 x 1.2 x .55 x 1.06 / 1.4 = 14.27 - SnS combo 2
440 x 1.0625 x .35 / 10 = 16.3625
238 x .24 x 1.2 x .55 x 1.06 / 1.4 = 28.54 - Revolving slice
440 x 1.0625 x .35 / 10 = 16.3625
=181.17
Citations:
Damage Formula: http://www.gamefaqs.com/wii/943655-monster-hunter-tri/faqs/59207
Hitbox Areas/Elemental Weaknesses: http://monsterhunter.wikia.com/wiki/Barioth#Analysis
Sword and Shield stats: http://www.gamefaqs.com/wii/943655-monster-hunter-tri/faqs/59581
Greatsword stats: http://www.gamefaqs.com/wii/943655-monster-hunter-tri/faqs/59580
Now, I would actually say this is biased in favor of the Greatsword, because the monster won't always be paralyzed. A 5-hit or 6-hit SnS combo is far quicker and easier to land than a lvl 3 charged Critical Draw. You really need to practice hitting that charged attack before you'll make a difference.
Also, there's a random 1.06 factor in the SnS calculations and a 1.05 factor in the GS calculations. For the SnS, it's a general 1.06 multiplier to all cutting damage done from the sword. For the GS, it's a really small sweet spot in the middle of the blade. Now, this sweet spot is hard to get, especially on a non-paralyzed monster. You really HAVE to make those hits count with the GS, whereas with the SnS, it's not so difficult. In singleplayer, at the least, you'll know that the monster is probably going to aim at you, but in multiplayer, it's difficult to predict where he will turn.
That is, if you are trying to land a lvl 3 charge. Otherwise, the damage is actually LESS than a full combo of the SnS (replace the 1.10 multiplier in the GS calculations with a .80 multiplier for a lvl 2 charge).
You could probably try some other calculations with the damage formula, too, but this is a decent theoretical example. Although, I admit, not many SnS users use the revolving slice at the end of their combo, even if they really should.