I agree. Headlines are actually the grabber in any content you post. What helps people to join your community is engaging and pertinent content -- this is difficult. If you just want randos visiting your site to pump up your metrics, you can rely on cheap tricks.

The issue arises when headlines' influence is in an order of magnitude.

At that point, even if you convert 3x less to your community, it's still worth it.

3000 visitors ---- 300 members (10%) 100 visitors ---- 20 members (20%)

I think that's what keeps aggregators afloat.