Yep - totally agree. I do think that's another benefit to "starting small" though with marketing via individual comments: your failures are a little less public than they would otherwise be. The most important thing is to be useful: if you don't have anything to say that leads to a "conversion" but do have useful input, that's great: give the useful input and move on. Only give a link to your work if it's genuinely very well suited to the response.
I also think people underestimate the amount to which really successful people have taken the approach of marketing via individual answers: for example, here are responses from the head of two compliance automation startups (SecureFrame and Vanta) with a total valuation somewhere north of $2B... duking it out in the comment section of a forum 2 years ago. Small marketing wins add up.