I still think that the 'Garlean' anthem is actually the original Ala Mhigan anthem that Garlemald simply took and replaced all references to Ala Mhigo with Imperial propaganda, and gave it back to the Ala Mhigans as "their anthem". After all, this is the first time we're hearing this theme despite the Empire being shown since 1.0, and that they already have a leitmotif which sounds nothing like it (Imperial Will, which does also show up in SB).

It would definitely explain why the actual music is also used as the BGM to Rhalgr's Reach and a few other things - it's truly Ala Mhigan, only it's been sullied by the Empire. It definitely suits the Empire's MO after all as a despotic autocratic regime.