I am not steeped in the lore of Magic the Gathering. Does anyone know and wish to share if the pantheon in the book is analogous to the classical Greek pantheon?
Sort of? It's not 1:1, but there's definitely a fair bit of overlap.
Gods you can swap out for their Olympian counterparts with essentially zero alteration:
Erebos -> Hades
Purphoros -> Hephaestus
Karametra -> Demeter
Gods you can swap out for their Olympian counterparts with minor alterations:
Nylea -> Artemis
Thassa -> Poseidon
Mogis -> Ares
Other Olympians' portfolios are split across multiple Therosian gods:
Athena -> Iroas (god of war) and Ephara (god of the city)
Apollo* -> Heliod (god of the sun), Keranos (god of prophecy), and Pharika (god of healing and diseases)
Zeus -> Heliod (ruler of the gods) and Keranos (god of storms)
Phenax is sort of like a twisted Hermes, emphasizing his "trickster god" aspect and acting as a reverse-psychopomp, being the patron of escapees from the Underworld, living and undead alike. (The other elements of Hermes's portfolio are absent, as far as I'm aware.) Then there are a couple of gods based on non-Olympian figures from Greek mythology (Athreos is Charon, Klothys is the Fates), and a god that doesn't overlap heavily with any Greek mythological figure that I'm aware of: Kruphix, god of both knowledge and the unknown.
There aren't any Therosian gods that overlap much (if at all) with Hera, Aphrodite, or Hestia. There
was a god that overlapped a fair bit with Dionysus, Xenagos, but he doesn't appear in this book, on account of being dead.
* One major part of Apollo's portfolio is absent, to my great sadness: there is no god of music. (Xenagos probably would have been the closest.)