Weapon damage on small and medium weapons.

Hi,

It seems to me that weapons like muskets and great swords should either do 1d8 when small or 2d8 when medium, for the game to follow the rules there seem to be for scaling damage dice to size.
Am i right? And if yes do we know why they do not?

Please help.

I didn't find the right solution from the Internet.

References
paizo.com/threads/rzs2qr8c?Weapon-damage-on-small-and-medium-weapons
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Thanks