Is writing a form of necromancy or seance, since through writing you can communicate with long-dead philosophers such as Socrates, Aristotle, and Plato and hear their thoughts and views the same way you can hear from people alive?

Nope.

With writing, they can communicate with you, but you can’t communicate with them. I can’t tell Aristotle “dude, you say women have fewer teeth than men—you were married twice, my dude, why didn’t you count?”

With a living person, the communication can be two-way.