Can anyone help me understand why second inversion triads are considered less stable than 1st inversion triads even though the intervals between the bass (chordal 5th), root, and chordal 3rd of a second inversion triad actually have more consonant frequency ratios of Perfect 4th (4:3) and Major third (9:8) when compared to that of 1st inversion triads with a minor third (16:15) and perfect fourth (4:3)?
The only thing I have found online that makes any sense besides several subjective, "that's just how it is" articles, is that the perfect fourth above the bass can sound kind of like a suspended chord? Although even this explanation seems a but suspect to me because there is still the sixth between the bass and soprano voices (to separate it from a typical suspended chord in root position) and the upper parts of the second inversion triad might still be displaced by octaves to make any kind of suspension feeling even less convincing. Any insight is greatly appreciated, thanks.