Contrary to popular belief, music doesn't "use" theoretical constructs such as the diatonic scale; listeners use them to interpret music.

In other words, the important fact about the diatonic scale is not whether it is presented explicitly in music, but that even when it isn't, it is still the basis for a listener's comprehension of the pitch structure.

(Also note that the pentatonic scale is a strict subset of the diatonic scale.)

This isn't an assumption. It's an empirical fact. Almost all music around the world uses a diatonic or pentatonic scale. The pentatonic favors such intervals even more strongly. The odds against this happening, if there were even one other equally-good possible non-harmonic scale, are astronomical. QED.

The work presented in this comment (link to audio examples) makes a convincing case that the consonance of "diatonic" scale intervals is simply an artifact of common timbres/sound spectra (which in turn are due to the physical makeup of most musical instruments), combined with familiarity. The music presented there sounds "consonant" and "harmonious" to me in a way that most atonal music simply doesn't.

(I am linking 4hodmt's comment here only because it's directly relevant and I don't expect its author to join this subthread. Any upvotes should be directed there.)

What about music that does not use those scales? And 1-3-5 chords are not present in all pentatonic systems. By what standard do you consider this music to be objectively superior? Is it something based on harmonicity?