Do you think there is a reason Garleans can't use magic?

[MikkoAkure]

But we see the Drahn (Au Ra) and Ronso (Hrothgar) in Norvrandt, and they're native to Othard and Ilsabard respectively.

Current locations of races on the Source doesn’t mean much after 13,000 years and a bunch of calamities. On the First, before the flood, Drahn had a nation where Ishgard is now.