Yes there is good bus services however it’s time that Dublin Airport had an extension to the DART.
Which other major airport in the world doesn’t have a good railway interchange.
I enjoyed the doubledeck bus service from Dublin airport into the city centre. Returning to the airport from Drumcondra Station, the bus to the airport never showed up. After 2-3 scheduled bus trips did not show; I finally split a cab with another person waiting for that bus to catch my flight to Glasgow. Another airport without a rail link of some sort.
To this list we can add Boston Logan (althought there is a free Massport bus to subway station or free Silver Line BRT to South Station (from airport only it is free of charge)), New York LaGuardia (although an Automated People Mover is proposed), Washington Dulles (the Silver Line Metrorail is under construction (behind schedule)), Houston, Los Angeles (an LRT (under construction) and APM system (proposed), Montreal (rail proposed), Rio, Sao Paulo--to name just a few.
It depends what you call "major" and whether you count railway stations slightly away from the terminals. For example, JFK is connected to the Subway and LIRR by the AirTrain but the rail lines are some way from the airport. Unless you call the AirTrain a "rail" service.
With six airline terminals (originally nine), JFK is difficult to serve by a city centre rail link that could place the station platforms near each terminal or set of terminals and provide the necessary track layout. The original JFK 2000 Master Plan envisioned a new central terminal hub in the middle of the Central Terminal Area with a single railway station, with APMs radiating out like spokes on a wheel to each airline terminal. Thus, a change of vehicles would be required to reach each airline terminal.
The current AirTrain system knits the terminals together with a loop track configuration, and shifts the transfer point to the Long Island Rail Road from a hub in the CTA to Jamaica Station. This has the added advantage of also providing connections to the subway and numerous local bus routes. Another advantage is that during peak periods, the LIRR track slots are maxed out, so there is no need to reduce frequencies on other branch services to accommodate LIRR trains direct to JFK.
Is this perfect? No. But given the multiple airline terminals at JFK (soon to be three as part of the JFK redevelopment), this is a decent solution.