I've used the Half - Garlean heritage as a sort of 'indeficiency to overcome', putting obstacles in his progression as a Thaumaturge. I've taken to it this way because, Initially I think people perceived Garleans incapable of using magic as a result of their Aether farming for Ceruleum, thus rendering them incapable to 'sense' Aether over the decades and so on, making it a hereditary, genetic thing. Once it became apparent however that that was less the case and they where just genetically inept to use Aether by default, I've had to make atleast one of his parents Garlean Migrants. Thus making his Origin of Birth Garlean, but his bloodline far from it.
By pure lore technicality (So far atleast), the only thing you cannot have is a pure-blooded, third-eye garlean mage. Aslong one of his parents is a migrant/Eorzean/Doman etc, It's likely that he too can be able to use magic, and eventually become proficient in it.
The indeficiency bit probably just aims to help you avoid getting into the 'special snowflake' (which is a term I abhor at this point, seriously) territory, as in adding background information not to be original, but to be unique. You may net a frown here and there if people find out your character has garlean heritage and is a mage, but it 'is' possible.
By pure lore technicality (So far atleast), the only thing you cannot have is a pure-blooded, third-eye garlean mage. Aslong one of his parents is a migrant/Eorzean/Doman etc, It's likely that he too can be able to use magic, and eventually become proficient in it.
The indeficiency bit probably just aims to help you avoid getting into the 'special snowflake' (which is a term I abhor at this point, seriously) territory, as in adding background information not to be original, but to be unique. You may net a frown here and there if people find out your character has garlean heritage and is a mage, but it 'is' possible.