I think its beyond our reach to discuss such things because those are devine relationships.
But for the sake of argument... We cant compare apples to oranges. there are different ways to reach the almighty and Sundarar chose his own style. Though most of his acts are not acceptable to common man, the title 'Vanthondar' clarifies all.
All the four devotees showed us four different paths of bhakthi Appar - andan-adimai Sambandar - thanthai-magan Sundarar - natpu Manivasagar - Guru-sishyan (rajni padam illa sir)
They showed us that whatever path we take, we can reach him. Such is the nature of paramporul.
This, I think we should see from the god's perspective and not from the human perspective.
Testing Appar with lots of sodanais (burning in sunnambu, thrown in the sea tied to a pillar etc) Taking sambandar as his child by giving dharshan with Uma and Uma giving the child her milk. Begging in the streets for Sundarar, which even a good friend will not do. Enlightening Manickavasagar as a guru..
So he comes to help in whatever form we are, but its up to us to decide whether we need to approach him or not.
Both shaivism and Vaishanism have similar examples all over the place. Krishna - Arjuna, Krishna - Yashodha, Rama - Hanuman, Rama - Guha, Rama - Bharata, Rama - Sugriva. Infact, Krishna is treated as a lowly charecter by Arjuna many a time and even after the viswa rupa dharshan, Arjuna treats Krsna as a Charioteer and not as the One. Yet, the underlying honest love is what counts. And Krsna promises us in the Gita, that He would to do what it takes to help His devotee. A promise is a promise, if we were to be a devotee :-)
Belief and Faith is key to devotion, it can be any form or relation.
God is most easily emotionally blackmailed so which ever relation you percieve with love and affection, that stream works.
1. Both S/Shri. Sundara Moorthy Nayanar and Thirugnana Sambandha Nayanar were considered to be direct divine creations ie., born with Gold spoons, So they had and enjoyed the Special previllages.
Hi sundarar sothanaikku utpattathu onnum kuraivilai. as a blind man and for some time with one eye. how god teased him. in thiruvenbakkam god promises to help the blind sundara and when he goes there with all hope, god gives him a walking stick.
it is parvathi as minnoli ammai who lights the sky with lightning and shows the way to sundara to reach kanchi. venketesh