In molecular orbital theory, it is often said that only orbitals with a) the same symmetry and b) similar energy can interact to a significant degree. I understand the necessity for the same symmetry, but the only explanation for b) I've been able to find is this one: https://www.quora.com/Why-is-interaction-strongest-between-orbitals-of-similar-energies
"It's fairly common to think of orbitals as static, but their phase changes in time. The frequency of this change is proportional to the energy of the orbital. So even if two orbital with identical shape and initial phase but different energy could exist, their overlap would only be constructive some of the time because they would not stay in phase. They can only be in phase all of the time if they have the same frequency, which is only possible if they have the same energy."
However, if this were the case, then every molecular orbital made out of AOs of different energy would be bonding exactly half of the time, while being anti-bonding the other half. Wouldn't this make it, on average, non-bonding?
Is there a better explanation for why the interaction is the strongest between orbitals of similar energy?