It is not that complicated. When the energy crisis in EU happened a few years ago, it demonstrated clearly that people and industry is willing to pay a years worth of energy bills for a single month to keep lights and machine operating. What this mean is that you could in concept give people free power for 11 months, and then increase electricity prices by 12x for the remaining month, and people would still pay it.

This also demonstrated through most countries in Europe that citizens will vote to have government that fix the energy market. Citizens do not want a free energy market that can raise prices to any degree, and its their tax money that fund grid stability.

This all mean that the cheapest form of producing energy do not result automatically in reduced energy costs for consumers and companies. The product that people pay for is not energy in a pure form, it is energy produced at a given time and given location. Make the energy free but the time and location expensive, and the total cost will still be expensive.

Transmission can help Ireland, but it can also hurt it by linking it to a larger market that can create a even higher demand spikes than exist in the current local grid. If the linked grid has locations which has higher energy costs than Ireland, then Ireland will subsidize those people by linking the markets together. Rules like highest price regardless of source sets the price, and higher amount of transmissions, also tend to result in more companies getting paid to maintain operations and thus more parties getting paid that is not linked to the marginal cost of producing energy.