Well, if all one wants is an "audience" one can simply report the results of their research on twitter. Much bigger audience. But that's not the point, is it? The point is that you want someone who knows their shit, to review your paper, and who will have both the knowledge and the motivation to engage with your work critically and help you see what is behind all those big blind spots we all have for our own work. I'm sure this happens with papers put on arxiv, occasionally, but my expectation is that just because the paper is on arxiv most people will not be that interested in making a serious effort to review it, and that it is much more likely that such a serious effort will be made by a reviewer in a peer-reviewd venue, particularly one of the top journals (conference reviews are a mess).

So, yeah, I disagree. The level of scrutiny one gets from putting their work on arxiv doesn't compare with peer review by experts in one's field.