You are right.Your 2nd example is a bit reductive.
At the other end of the reductive "Why have a single garda in a station in each parish" is "Why not just get rid of Garda Stations altogether and have them all controlled by one central control room"? I'm sure you can see that would be just as impractical as having a single garda at each station in each parish waiting to react to local problems.
There should be a happy medium that would see sufficient gardai out and about locally, with local knowledge, to help stop crime.
Just politics will not allow for Garda stations to close as it portrays a certain image amongst the public who think Gardai operate like the fire service.
I don't think they have the numbers anymore for that old fashioned view ot policing