Keep in mind that 3.0 already had weapon sizes. And I'm sure there were some powergamers that tried to exploit them by picking the optimal combination of size and weapon.
The only thing 3.5 adds are (1) some consistent rules on how these off-sized weapons work, and (2) some much-needed restrictions on their use.
PS: Even if your DM doesn't want to use the optional equivalency table in the DMG, I assume it should be fairly easy for a weaponsmith to convert an off-sized weapon to an equivalent one that's appropriate for your size.
The only thing 3.5 adds are (1) some consistent rules on how these off-sized weapons work, and (2) some much-needed restrictions on their use.
PS: Even if your DM doesn't want to use the optional equivalency table in the DMG, I assume it should be fairly easy for a weaponsmith to convert an off-sized weapon to an equivalent one that's appropriate for your size.