Leto and her sister Asteria (interpreted at times as being associated respectively with the night in which all things are hidden and the stars) are daughters of Koios (the axis of the heavens and associated with a great heavenly dragon) and Phoebe (bright goddess who in some mythic variation associated with Delphi and its respective dragon). These children of Ge and Ouranos are therefore fundamentally associated with dragons and hidden obscure knowledge given that the north star is the center of the revolving heavens by which men determine their fate and navigate both on sea, sowing crops, and through life…and Phoebe’s association with the oracle and as a luminous goddess being a revealed.
It is perhaps natural that we woukd see Asteria as potential foremost heir given that her name connects her directly to the stars, and her own daughter Hekate being one associated with hidden knowledges and rites. Yet even as Leto’s name commands respect of that which is utterly hidden ans unperceivable, it is from her that is issued the voice of divine truth and prophecy. Yet it is important to remember that Delos who was first nurse to her children was none other than Asteria. So the development of the domains of her children are linked too to that if her sister and may even have some further bearing on the very close semblance of Artemis to Hekate. Yet where as Hekate is directly connected to the mystery of the hidden for which she is supplicated and served likely through the occult nature of mother Asteria established. Artemis and A pollon are revealers and illuminators of the mysteries as they originate from the dark womb of their mother. Leto can thus be understood conceptually as a place and time lacking of illumination. Beneath the night sky, in the depth of the cave, and the bowels of a swamp where her son too has received worship especially as Pythios.
In short Leto’s (and her children, sister and niece as well) by her parentage is descending and connecting specifically on the prophetic/illuminating, raw and wild life giving and destroying force of Ge (unlike her cousin Rhea and subsequent Demeter and Zeus who tend to be more specifically connected to man controlled agriculture). Thus it is easy to see how the union between Leto and Zeus yielded Apollon and Artemis as gods who reside somewhere in the middle.