The ICs being fried wouldn't cause low volume, you'd just have no output like your other one.
Most likely either you got a "disco" parts placement and they put in too large or small a resistor which is choking off the volume or reducing the op-amp recovery gain after the tonestack or it's the bypass circuitry just bleeding a bunch of the signal to ground. Hard to tell without it on the bench though.
Do you do diagnosis and repair? from what I can tell it's all original, at least no parts to me scream newer/aftermarket but if nos stuff has been used, I can't possibly tell.
