I think you definitely do have a point, but it's also a matter of taste. Yes, I do assume that characters we only note in passing have more to them if we'd look into them - just like that newspaper seller has a life, emotions and relations of his own, which we know nothing about because our lives only intersect so very briefly. That level of one-dimensionality I have no problem with at all.

It's okay to not get everything served nicely and finished, and I certainly don't mind using my imagination to fill in the gaps. But I happen to like character-driven stories, and I do tend to get bored when I get the feeling that a writer really couldn't care less who is going through that adventure they're writing. I don't need to know everything about a character, but if they're at the center of the story, I would like to see enough to get a feeling of what makes them tick, why they are doing what they're doing, and I love seeing how they develop through the things they experience. There will still be gaps to fill and imagination to be used, because no story ever covers every aspect (or if they do, they probably would never get any plot done at all, and probably not even then). So I find saying people who like multi-faccetted characters just don't want to use their imagination (whether for laziness or lack) is not really fair. It is a matter of taste and preference, and liking them multi-facetted is just as valid as liking them more open and not predefined (or one-dimensional, if you prefer). Just as liking plot-centric stories is just as valid as liking character-centric.
Sure, they're usually not equally fashionable at the same time. But definitely equally valid.

(I don't know The Professionals, so can't say whether I find this character Doyle specifically one-dimensional and whether it would bother me in that specific case.)