I wonder what the SEO value of a forum + some addon, vs WordPress + Yoast (or similar) looks like. Boosting the SEO of a forum is hard, but a blog is a different endeavour.
When it comes to a forum, the structure and organization can be a bit more complex than a blog, which can make it harder to optimize for search engines. Typically, free forum software doesn't have much built-in SEO features like meta tags, sitemaps and XML feeds, which are essential for SEO. Paid softwares like Xenforo and IPS do though.
On the other hand, a blog built on a content management system like WordPress, generally has more built-in SEO features and a simpler structure, making it easier to optimize for search engines. Plus, there are a lot of popular SEO plugins available for WordPress like Yoast, which can help you optimize the blog for search engines by providing features like keyword optimization, meta tags, and XML sitemaps.
While it might be a bit more difficult to optimize a forum for SEO, it's not impossible. By using the right tools and techniques, such as using a forum plugin that includes SEO features, creating a clear navigation and organization, and creating a sitemap, you can improve the SEO of your forum. But, if SEO is a primary concern, then a blog built on a CMS like WordPress with a SEO plugin may be a better option as it has more built-in SEO features and a simpler structure.
There's not definite answer on this, but I think it's safe to say that a blog will out performance SEO over a forum in most cases. But forums don't need to have a blog with the right add ons nowadays.