You can't directly compare numerical values of "idea" to "idea * execution": the two are conceptually different things.
To abuse physics terminology, the units are different. In physics, a mass of "12 kg" is not in some sense greater than a force of "6 Newtons", even though the two are related by F = m * a. Similarly here, dragonwriter is defining "quality = idea * execution", so there's no reason to expect that the numerical value of this notion of quality should be directly comparable to the numerical value of either of its components. (Comparing the value of "quality" defined this way to the value of "idea" would require assuming some specific value for "execution" for the comparison to be sensible. If you just compare the numbers directly, you're assuming perfect 1.0 execution, which probably isn't what you intended.)
To abuse physics terminology, the units are different. In physics, a mass of "12 kg" is not in some sense greater than a force of "6 Newtons", even though the two are related by F = m * a. Similarly here, dragonwriter is defining "quality = idea * execution", so there's no reason to expect that the numerical value of this notion of quality should be directly comparable to the numerical value of either of its components. (Comparing the value of "quality" defined this way to the value of "idea" would require assuming some specific value for "execution" for the comparison to be sensible. If you just compare the numbers directly, you're assuming perfect 1.0 execution, which probably isn't what you intended.)