Trying to do approximate math for this is difficult and the difference seems small but greater than trivial. The larger point raised by the author is that the more packaging, dyes, adverts, etc. that a product has associated with it, the more likely a consumer is to buy it(??), and each step of the marketing-to-consumer pipeline costs more environmentally and energetically.

This is not a condemnation of advertising or marketing. In order to sell an environmentally-conscious product, you still need to sell the product.

It might seem impossible but there probably are long-term solutions to much of consumer waste. We aren't even really trying that hard overall to cut down on this and amazon et al are world leaders in packaging and return waste. There might not be easy answers but even partially solving the consumer packaging problem would cut down on landfill/recycling use.

It's a good thought exercise to imagine how you would sell razor blades without any packaging.

Cartridge and (quality) safety razors don't last the same amount of time. The additional plastic on a cartridge doesn't seem like much, but when you look at the millions of cartridges disposed in a year, it certainly adds up. Compare the packaging and space of 100 safety razors to 100 cartridges and you'll see an enormous difference. This all stacks up to a bigger impact in packing, shipping, etc.

Not to mention the disposable whole-stick razors that some people use (those are terrible).

You also don't provide any data to back up your claim that the total share of waste from all cartridges is trivial. You can't just hand wave this away so easily.

Once people have forgot about the less-convenient alternatives, they can't accurately price convenience anymore and will just pay whatever is the market rate for the convenience product (be it coffee pods or razor cartridges).