Removing blogspam increases quality, no question. I keep meaning to write better feedback for Lemmy with what I’ve learned over the years, but blogspam is a hot topic of mine so I’ve listed some thoughts here.
One addition to your list is insistent self-linking to the website itself at many points through the story, very little sources outside of themselves.
Blogspam usually copies or re-writes source content that is usually linked in the story. A big problem with Linux news are the re-writes of mailing list posts with added opinion.
On top of ads, referral links are common, especially by gaming and hardware blogs.
Finally, and it’s hard to describe, but a lot of blogspam sources have a cult following. If they take action to harass people because their content was removed, they should be banned entirely. I’ve had two website owners get their little cultists to harass me because their content was removed.