Plenty of examples in the US. Philly is not the capital of PA but it’s great, while there’s feck all in Harrisburg. Capital of Cali is Sacramento, not LA or SF. Albany New York another example. Baltimore dwarfs Annapolis here in MD (though Baltimore is shite anyway so bad example). We’d need to offer incentives to move private sector investment away from Dublin rather than picking a new capital I reckon. Difficult with all the existing infrastructure though (airport and ports especially) probably.
So many country towns dying around Ireland though. Where my grandmother was from is like a ghost town now. Grim.