Q: why is the 5th of a chord so unnecessary compared to the root, the 3rd, 7th, 9th etc? is it just so damn implied by the root that it's often superfluous?
A: i'm pretty sure you are talking about chords with more than 3 or 4 notes. in that case, i guess chords tend to be happiest when there's only 3 or 4 different notes at a time, or less. but sometimes the 5th above the root is actually the most important. it seems like you are probably just having the kind of day where you are directing your attention to certain kinds of chords and contexts where the note best described as the '5th' of the chord happens to be the unnecessary one