Australia managed to do it without the agreement of other countries. It wasn't any bullshit about competitiveness that caused the repeal either. It was pressure from the coal industry.
Yes any country could do it alone, but all it does is slightly reduce global demand, Australia being a fairly small country population-wise likely didn't make a dent. All other things being equal it doesn't leave fossil fuels in the ground, just increases the amount of time before we extract them. That does buy time for the human race to find a lasting solution.