I think a clearer way to say what a lot of people are bothered by with that example is that in order to sell those recommendations you need:

a) to have a lot of marketing expertise

b) to be known well enough for your marketing expertise that people will take your suggestions as valid

Most tech people have neither one. Hell, most marketing people have neither one, half of the rest on my have b) but are actually incompetent in their recommendations, and only the last little bit have both.

Being a consultant is marketing, there is no way to be an engineering consultant. Engineers work for consultants, not as consultants.

If you want to make the big bucks, you have to do what businesses care about, not what you care about.