I have been using this process for years.
Our Lab was the first lab worldwide to offer Digital fibre Murals on Silver Gelatin Paper, we started with Agfa Classic which is not panchromatic.
The Paper Harman introduced latter has an extended red sensitivity.

I am not sure why, other than the red sensitivity may have been needed for the laser exposure to work. I think here lies your answer.

I work exclusively with the Harmon Paper for laser and exposure, I do not make RC prints though and that is consistent with my enlarger work.