GDP per capita is fairly meaningless, except as a political willy-waving excercise. Average wages are rougly equvilent at just over $55,000 but unemployment is 3.7% in the UK vs 5.4% in Ireland. Ireland’s higher gdp per capita in the face of this reflects the fact that they have a much higher proportion of their national wealth concentrated in fewer hands, which is not a positive. Net migration from Ireland to the UK is MUCH higher than the other way around, and I would probably say that the vast majority of “Brits” emmigrating to Ireland do so because they are already Irish by blood and have simply moved back to their Irish homeland to be with family.
https://countryeconomy.com/countries/compare/ireland/uk?sc=XE34
Yet the average wages are the same. That’s doing well.
As to net migration between the islands - do you have those numbers anywhere to view?