A headline has always been an attempt to sell an article access to headlines and has a long history of freely accessible for this reason. Publishers WANT links to their article to use their headlines because that is how the articles are sold.
You talk about the 'atomic unit of journalism' being reporting... but that isn't really a meaningful assertion. What is meaningful is that facts are not copyrightable (which is good.) If you are selling access to facts as your product, you have to differentiate yourself on either storytelling, curation or speed.
Notably, the California law covers all links, not just those that include a summary or headline.
I don't think the crisis has anything to do with aggregation. I think the crisis has to do with how money is spent on advertising, how much of that money Google is able to extract via their monopoly, and the degree to which we've allowed capital markets to gut such a vital institution. I think the EFF report linked in the article does a much better job of breaking down the issue, even if I don't agree with every recommendation it makes or think they are sufficient.