Own observation from our own sites rankings.
Blogger content doesn't have to be great and or human readable to help build your site's rankings.
I assume better content is more readable, clickable, searchable and mostly sharable.
Emphasis should be on formatting and write uniquely as possible.

Length is debatable. 500+ words should suffice each post
Quality builds efficacy. Q
uality Content that ensures it's an asset for your business and helps your audience
Page speed optimizer. Instant boost.
Quality backlinks and guest posts should improve rankings.
Keep in mind new sites would be a waste and only fully optimized sites should buy links.
Increasing traffic volume - improved rankings.
Increase keywords - improve rankings
Upgraded Server and WP core and design only UI and UX improvements no change in rankings.
SEO tweaks that are less important:
Spending time fixing all the site errors if not critical errors could be a waste of time.
I did a SEMrush audit and went through all the fixes.
Little to no impact on site performance or rankings.