I did this overlay a while ago for a Reddit post about this topic. My biggest regret is ARR (my only one, really), is the loss of scale of the world. While the copy paste was a bit of an issue, I loved the vastness of the zones. Now the city states feel more like neighborhoods. If you look at all the parts that were cut out of old Coerthas, there is a massive chunk missing between it and Gridania. And it's not like you can just retcon an entire zone between two existing zones.