About the lingering resentment between Gridanians and Ala Mhigans, don't forget that elezen are stated to live up to around 180 years... so most of the elezens that were present during war times are probably still around, and that Ala Mhigo was was basically Garlemald back in the day, in that they were a massive invading force which forced the rest of Eorzea to unite to fight back.