1 Guest post will not skyrocket your site, there are hundreds of factors, of course, a niche related one is more powerful than a magazine-style one, but in the end, the number of them counts more, from where, to which site, type of content and so on.
Example: Forbes vs Medium; Medium is more powerful, Forbes is just for branding, still Forbes costs up to 2k a post, while Medium is free with good content. So, link building it's more than just building a guest post.