The Ancient Dragons within the Ancient Temple are the one exception to the 50% rule as they are one of 3(?) enemies explicitly weak against Gravity (the other 2 are in the Shinra Mansion). The (HP/2)*1.5 is likely correct in figuring out the damage. So... (1.5 *.75)= 1.125= more than enough damage to kill in one shot.
Re: 50% Demi+ Weak= ...50%
The Ancient Dragons within the Ancient Temple are the one exception to the 50% rule as they are one of 3(?) enemies explicitly weak against Gravity (the other 2 are in the Shinra Mansion). The (HP/2)*1.5 is likely correct in figuring out the damage. So... (1.5 *.75)= 1.125= more than enough damage to kill in one shot.