Well, a large portion of my magical practice has always involved petitioning deities in some form or fashion.
I'm going to discuss from my current endeavor as it will help me process ideas.
It seems ancient Greeks and Romans were also divided on what constituted as magic, medical, and religious practices. The PGM illustrate that Deity and Spirit work was the thing, honestly it was the only thing. Magic didn't work unless you sought the aid or abused a spirit into giving your desires. The difference being that the magician or witch tends to invoke powers of the chthonic, such as Hekate or Persephone, where as the priest, philosopher, or holy man invoked the powers of Ouranic deities. (most of the time) The religious man would come to the deity in piety, but the witch would seek to command them. (sometimes)
Apollonius of Tyana, a miracle worker and philosopher, pretty much gives this idea in The Life of Apollonius of Tyana , well at least Philostratus does. When accused of magic (he helped avert the plague of Ephesus), he says that he just prayed. Pretty much stating that a prayer to Hercules, then later a temple construction, was not magic as it did not involve infernal deities.
To battle the idea of witches and magicians being spirit abusers, there is the PGM XII (245-253) which admits to the greatness of a unknown powers, probably the Zodiac. Then, there is the PGM III (1-25). This is a small thanksgiving prayer. So, both of these show some degree of humility and piety.
From the scenes of Simaetha and Medea, they obvious implore the gods, a large number of gods and not all of them chthonic. In the case of Medea, one could argue she is divine or at least more than human, so this is okay to do. But, Simaetha is not. She's just a witch. Yet, to me, she doesn't read as commanding the spirits. Of course, this is a story written by people who may have had only a vague understand of magic. At the very least, we can draw some ideas about the cultural thoughts on magic.
Personally, I feel it boils down to your personal identity. What do you want to call yourself? Where do you feel you belong? Obviously, not everyone who petitions a deity about something will call themselves a witch. Not everyone who meditates, seeks oneness, and/or petitions for things calls themselves a magician. Identity matters.
