That's nonsense. Most of the house can be built off-site in a factory with automated lines. First fix electrical and plumbing can be done at that stage. The assembly of the units on site can be speeded up by using the correct power tools instead of 18th century hammers.
Then proper QA and QC can be carried out at the time of manufacture so the purchaser isn't relying on our third rate tradespeople to fit windows, plaster walls and hang doors. Who knows, the plumbing mightn't leak and the doors and windows might open and close properly!
The only major element that needs to be manufactured on-site is the foundation and that is done using heavy equipment.
Houses in Ireland are built in the same way as they were 50 years ago. At least half of the on-site labour cost can be removed, maybe 75%. The off site labour can be done more efficiently and to a higher standard.
We need to build houses the way most of Europe and North America does. The site is what's valuable so the house itself should be able to be changed every 50 or 100 years without a massive financial and environmental cost.