"Now we have 2 divisions which work well(ish) and interest has never been higher, with a fully professional premier division. If it's not broke don't fix it."
I agree with your post, especially the above. I also am excited with the FAI's plan for a new National League third division. Hopefully it gets going as planned and as with all new ideas, it will have its issues at the start.
Significantly, the real intention is to create new competitive platform and pathway for non-league clubs which should also make the first division more competitive.