Benito You can always install WordPress and connect it with Flarum to manage users. To display the news in the forum, you can use the WodrPress RSS and NewsFeed extension.
https://discuss.flarum.org/d/27214-newsfeed-add-a-box-that-show-latest-article-from-a-rss-url
About what is better or worse for SEO... I disagree. Flarum works very well at the SEO level, everything is well structured and marked up, and the Blog extension does what is needed if you combine it with the SEO extension. The rest of the functions are easily solvable without plugins (Rewrite URL, Pings...etc). I've been working on professional SEO for years, and while the Flarum Blog extension has a lot of room for improvement, it does the basics for ranking articles. If you need help to modify it (Schema, inernal links...etc) you can ask in this thread and I will try to help you.
I think that having everything integrated (Forum + Blog) is a very big plus that WordPress simply can't provide. Future SEO is going to reward comments and user-generated content a lot, you can read a bit about that with the "Perspectives from Google Search" feature. So a single account, integrated comments within the forum and all in one CMS will be key to increase participation. Here are the search results for my Flarum site in just 6 months.
However, the blog has a lot of room for improvement. For example, it doesn't work well when it comes to taking the user to the last comment of a blogpost, nor does it allow basic things like being able to use schema markup for the author (essential for SEO) or edit the authors' biography. There is also no option for the user to choose from Flarum what he wants on the front page (Forum or blog).
