The law is you stay left unless overtaking traffic in the lane that you are in. It is illegal for them to join in front of you at a slower speed.
That said it does make things easier for everyone if done correctly, but the problem is the idiots who pull out into lane 2 obstructing faster moving traffic in that lane.
Nothing wrong with moving lane to overtake joining traffic once it's done correctly.
You're trying to real hard to infer lane hogging holding up impatient drivers....
As I said earlier UK drivers move left much more often by the book and (in my opinion) it makes for a far more chaotic experience. Cars constantly switching lanes. Irish motorways are far less stressful and more predictable to drive on.
I would not say Irish rules of the road are perfect. Ours are mainly cut and paste from older UK rules and updated very slowly. Other countries have some rules I think are better.