Still Guest Post is effective for ranking?

Low-quality guest posting has never been effective, now seeing as we never set out to write a low-quality post it is common that we think our posts are great quality but in reality, they are often poor. Grammar and spelling is also so important.

I don't mean to sound rude, but if your guest posting is to the quality of the question being asked here, then it would be deemed inferior quality. Yes, I can understand what you mean but it would not score highly in googles eyes and remember google is attempting to show the best quality there is available to the question asked. 

It is to be always remembered that Google always prefers the content which is the most relevant and quality-focused for the audience and will only rank them accordingly. So, yes guest posting is still capable of doing wonders provided you focus on the content while maintaining the relevancy.

hire some content editors and ask them write the best content in you niche then publish it on your site and start outreach that will work better than guest posting  

Read this https://moz.com/blog/adt-keyword-ranking-case-study

Guest posting is relevant and effective you must do some quality work and will see the results. 

Guest posting is a good way to a good result of SEO. Creating these backlinks can help you climb the search engine ranks over time.