I don't know where this story of the train not being as nice comes from but it is basically claptrap. There is nothing at all wrong with Irish Rail.
The thing is that you have to catch a frequent direct bus from Dublin Airport to Heuston Station (4 an hour), €6 each way, before catching the train. The train is then broadly every two hours- https://www.irishrail.ie/getmedia/81529cec-6419-43db-9b2d-4563775766e6/06-Dublin-Galway.pdf
Because you can't book an Advance rail ticket, due to the vagaries and uncertainties of international air travel you end up buying one at the station which costs €30.45 Single or €43.35 30 day open return.
The bus is €17.50 each way and runs every 30 minutes. It is marketed as Citylink but is run by an independent company called Callinans as a franchise. Bus Eireann no longer run that route, but do run the Galway to Doolin bus. It doesn't matter how frequent the bus is from DUB to Galway when the Doolin bus #350 only runs 5x a day- at 0800, 1000, 1300, 1500 and 1800.
The 350 leaves from the Railway Station, not the Coach Station where the bus from DUB arrives- although they are only a short walk apart.