Well, the title here at HN implies something else than the study shows.

If blue light actually impaired vision, that would be very notable. It would mean that removing the blue 'channel' for an RGB image would improve acuity. This is not what the study showed, however.

It is mainly just the basic fewer cones bit you mentioned. Which, btw, is easily experienced if you ever look from a distance at neon or led signs that only emit blue light. They'll persistently look out of focus when compared to their surroundings.