Getting public readable content indexed by google and other search engines

Looking for some advice. I need to get the public viewable content of the site to show up in google search results.

After searching here, as well as googling web, I found this page where the solution is to add the rss as sitemaps in google webmaster tools

http://community.elgg.org/discussion/view/1192327/elgg-seo-google-not-indexing-blog-articles

I tried adding it but get a not found error(404), so I think I am not providing it a proper rss feed

 

I searched again and found this for an older elgg version

http://community.elgg.org/plugins/385064/1.0/planphoria-elgg-siteindex-generator

This which looks like it will work with modern versions

http://community.elgg.org/plugins/1077524/0.3/auto-sitemap-dinamic-seo-sitemapxml-generation

and even this, a 3rd party program

http://enarion.net/tools/phpsitemapng/

I am running 1.8.16

How does the community get their content indexed properly within a short time period?

Are any of the plugins here useful?

Why was this not functionality not built into elgg core(or am I missing something)?