Well, the worse your shaves are, potentially the more you need to see a dermatologist because of ingrown hairs, razor burn, and the other assorted problems cartridges cause. I'd make the case that perhaps your dermatologist wants you to shave with those products to help keep him/her in business.
I will ask him for his reasoning.
I noticed he had a Gillette Fusion coffee mug, baseball cap and mouse pad......... Hmmmmmmm.
I second that thought. Now you have an official second opinion about needing a new dermatologist. Tell him someone said "the more dermatologists, the better."
Ask him for a detailed, scientific/dermalogicial explanation for his recommendation.