Qube is simply wrong (although this is possibly just a difference in semantics). Chlorine pentafluoride comes to mind. PCl5, SF6, the list is endless...
O=S=O ?? So, if I understand you, the sulfur atom, which you surely KNOW is less electronegative than oxygen, is what? - surrounded by 10 electrons? (that is :S(=O)₂ ). comparing the difference in electronegativity, is a zero formal charge reasonable? Ozone with the same (formal) bonding has a dipole moment of 0.53D compared to SO₂ 's 1.62 D. So, if that isn't telling you that there is a LOT of charge separation, I don't know what could. Why will having a zero formal charge result in the lowest energy state ("is advantageous"). News to me. Wikipedia says:" a formal charge is the charge assigned to an atom in a molecule, assuming that electrons in a chemical bond are shared equally between atoms, regardless of relative electronegativity." IOW, "regardless of energy", since electronegativity is a proxy for the extra energy of bonding 'due to' quantum mechanics and was an early (fairly successful) attempt at including canonical ionic contributions to bond energy (ie at 'explaining' why bond energy of A-B is usually greater than the average of the A-A and B-B bond energies). Formal charge is an accounting 'gimmick', and should be viewed as having only very narrow utility. (The same can be said for electronegativity, but formal charge is more often used in organic chemistry, while electronegativity is more often used in inorganic, I think.) (Both can be (carefully) applied, but the reality is that neither are as good as Density Functional, Molecular Orbital, or Valence Bond quantum mechanical treatments of what is inherently a QM problem.) Up till about the 1990's, chemists relied on a lot of rules of thumbs like these, DFT has allowed them to instead rely on (more accurate) calculations and models (but at the expense of intuitiveness). Instead of relying on our crude mental models of the geometry and bonding of chemicals, we can instead look at the results of DFT theory to determine where electron density is. Its an attempt to fit more classical electrostatics to what is properly only solved with the use of QM. As a student, it makes sense to learn the easy stuff first, and then move on to better (but more complex) stuff. The real foundation of chemistry IS quantum mechanics, but that is beyond the mathematical competence of most undergraduates. At the same time, there is a boat load of chemistry which can be (more or less) put into some sort of coherent body of knowledge without knowing the QM. Learning about bonding begins the process of connecting the two.