The 1,500 hour rule was pretty arbitrary, but at the same time it forces new pilots to get experience flying outside of a training environment. Those hours of flying without a flight instructor next to you is where you really build your Aeronautical Decision Making, and you probably make some bad calls that you get to learn from because of the lower stakes involved. Especially since these days a new hire is likely to be a Captain within two years at a regional, I do think those extra hours really make a difference.