You can’t compare T Third with the Luas. The Luas is a bad substitute for commuter rail, which should have been built instead. Many of us knew it would become a victim of its own success; the trams are 131 feet long and 7.8 feet wide, and the intent is to squeeze 360 people into that little tube. (Before that, they were operating 98-foot-long trams, with a stated capacity of 256 passengers; this is the same as squeezing 128 people into a 48-foot bus, which is the US standard length for a city bus IINM.) You’ve also distorted the ridership figures; the Luas is two lines, not one.

Incidentally, the T Third has high platforms, which jacks up the capital costs. There was also probably a lot of utility relocation necessary, due to the tracks being built along the street sides; the line also requires a lot more traffic signal priority hardware and software due to this. (More capital costs.) Stations are also a quarter-mile apart on average; on the Luas, they are an average of two miles apart (so the average speed of the Luas is actually comparably pathetic while the T Third is remarkably fast; the Green Line, the one you cited for average speed, was built on the old railroad right of way, so that’s an apples/oranges comparison in many respects). Also, the T Third vehicles have couplers, making it easier to build a longer train; the Luas vehicles have no couplers, apart for some emergency drawbars that are used only in the instance of a tram breaking down, to push or pull the broken-down tram.