I agree it could be simple to define a subset of units to simplify the game.
You would however need to use more than the core box (to have enough choice).
Trying to play without troops and focusing on Gods and Heroes without troop abilities (like bolster, leader, phalanx) may be possible :
Gods (very few choice) : Ares, Hephaistos, Hera, Hermes
Titans : all except Gaia (so 4)
Heroes : Achilles (both), Aegistus, Andromeda, Antaeus, Atalanta, Autolycus, Echo, Veteran Heracles, Icarus, Marsyas, Medea, Pandora, Paris, Periphetes, Perseus, Sysiphus
Monsters : all of them I guess except Minos