Hesiod attempts to derive the name Τιτῆνες (Titans) from τιταίνω (stretch, strive) (Th 207-). Possibly the above picture is an explanation of his view.
In ancient Greece, just as most everywhere, honor and status are age dependent. Siblings of the same sex are ranked according to their age and the first-born has a special place of honor. If this is true of humans, it must be even more important among the gods(1). So in a well-ordered society gods and people would find a husband/wife of their own rank. Here we see how Titans of very unequal status marry. The youngest, Kronos, who is to become King of the gods, acquires the second-ranked Rhea as a wife. All this goes without comment in the Theogony. I will call a relation like Kronos-Rhea an upward relation (from the male p.o.v.) and one like Okeanos-Tethys a downward relation.
These things do play a part in the human world. For instance the trope 'hero wins the hand of the princess' can be viewed as an upward relation. The king (or his son) are conceptually the 'best men' in the community(2). If there is a problem they cannot solve and the newcomer can, the latter has shown himself to be better and therefore worthy to be king. The princess is his prize, his future kingly status depends on her. The reverse is the case in Cinderella-like stories: the servant-girl who marries the prince.
The range of meaning of the up/down picture extends even further. There may be negative connotations as in rape (upward) and prostitution (downward). But this is not the web page to go deeply into these matters.
But back to the gods: all this would not seem very relevant if it were not for the stories about the demi-gods (ἡμίθεοι), the sons and daughters of gods mating with humans (WD 159-60). This important group (found also in the Old Testament) plays a pivotal role in many if not most of the Greek myths. Relations between gods and women, or goddesses and men, are also either upward or downward. Achilles sprouts from an upward marriage, Peleus and the goddess Thetis; the result is a king. Heracles comes from a downward one: Zeus and Alcmene; the result is a servant: the child inherits the mother's status. I wonder if there is an ancient theory behind this, that these unequal relations are the cause of much trouble in the world.
There is another point about these demigods - they are not there anymore. They were beautiful - they are gone - they are worshipped. See scapegoats. Let us speculate a bit further on that. Both in Homer (Il 12.23-) and Hesiod (WD 157-, about the fourth generation who now live on the Isles of the Blessed in a kind op poetic aside, the demigods are looked back upon as glorious but gone. Is is possible that the semi-divine heroes themselves, as a class, are being scapegoated away(3)? See also the Hesiodic Catalogue of women, book 5.201- with fragmentary but interesting references to Zeus' plan to get rid of the demigods, threats of war, the necessity for the Ionians to 'choose the sea' and Apollo's role in this.
This myth is an obvious borrowing from Hurrian or Babylonian myths. M.L. West prefers an early date for the transmission, Minoan or Mycenean, among other things on the grounds that the story is completely absorbed into Greek tradition: names of the gods and of places are completely hellenized. West asks the question:
"Is it to be supposed that at the very beginning of the orientalizing period a complete theological myth was taken over bodily from some Near Eastern source, translated completely into Greek terms, and immediately retailed by Greek poets and the very priests at Delphi?"(5)
I would say yes, that is exactly what they were doing, not only with this myth but with the whole Olympic religion, the city-state politeia, the Panhellenic revival, the alphabetic script, not to mention the Great Epics. All of it gives an impression of being based on adaption of some Near Eastern (Phoenician?) know-how of organizing a modern state. To be sure, there must have been religion in post-Mycenean Greece. Important to the people but formless, local, based on traditions about gods, people and places that we still find in the Olympian kosmos but relegated to the lower echelons. The new religion was not traditional, it was consciously created (using preexisting names of gods) for political purposes. These people knew exactly what they were saying and why.