Just gaining Might does not make something Immortal, which I broke down in this post. Being immune to aging (from Might) =/= immortal. There is a pretty extensive list of differences between them in the game.
For learning, things with Might have an XP penalty (can be overcome with Vis) and have no problem learning spells, while Immortals don't gain XP or new spells beyond a season without storing it in enchantments (losing it if the enchantment is destroyed). So Might can still learn while Immortals can not.