That's comparing the very cheapest advance bus fare to the walk up fare for the train. I'm sure Michael O'Leary would be proud
Using Cork as an example, you could make the same argument for travel to Dublin City Centre, yet 2.5 million use the train between the two cities every year, so if the option is there, plenty will use it. Of course, Cork has the advantage of a pretty fast train service to Dublin that beats the bus by 45 minutes. I doubt the numbers would hold up for other lines.
I did say at the very least double which is 40 euro and given the extra distance I would add another 5-10 to train fares as Irish Rail would be forced to cut fares to Heuston otherwise. They have have a good sale once or twice a year but my point still stands.
Your 2.5 million figure is incorrect, the way the figures are bundled together it makes for great reading but it's far from reality.
As for speed the bus can do in 2h45-50 at night and the train takes 2h30,(+30 to airport if happened) even the new express has failed to be on time, attract numbers and has made a lot of other people angry. The express is bleeding money but it won't ever be scrapped nor expanded....