How could Aldo complain? 3 of his last 5 title defenses were in Rio. He hasn't fought outside of the America's since 2007.
"I'm sure that I'm on[e] of the best of all time. I don't see where am...yet. When I stop, I want to be the greatest of all. I still seek some achievements. I'm the only UFC 145-pound champion in history, and I want to keep [it] that way until I retire,” Aldo said in an interview with Combate, which was reported by Fernando Arbex of Bloody Elbow. “I also want to break all the UFC records in a way that my name will be printed forever."
The only way he goes down as a GOAT is taking any fight, anywhere.
Also, the largest indoor arena in Ireland is the 3Arena, with 15k capacity.. For context, Jones v Cormier had 11.5k in attendance, Werdum v Hunt had 21k. Rio's Ginasio do Maracanazinho has a capacity of 11.8k, and Aldo's last fight had 11.4k in attendance. I don't think that capacity will be a determining factor as average UFC attendance is between 10-15k. I think the decision has more to do with the amount of energy the crowd generates on the broadcast, and I don't think there is a huge difference between Rio and Dublin.