Yes, blogs are definitely worth it - but there's no denying it is certainly time-consuming because the blogging industry is overcrowded - to stand out and create something that hasn't been done yet is challenging.
In the case of videos as compared to text-based content, ranking is certainly easier, but mostly for How-to content. For detailed analysis and information, people still tend to lean towards blogs - it's more of a collaborative strategy. You create a buzz around your actual blog with video content - it's more like writing a long blog for your website and then using a Medium article to promote it. Similarly, brands are using videos to lead their audience to the website - it's mostly referral traffic.
Now, coming to your third question, updating old content is a part of hygiene check - of course, if I have a new website with 50 blogs and zero guest posts, I hardly need modification. But a website that is old and has lots of content, needs regular checks - and updating old content as per changes in the niche and industry is a common hygiene practice. Understand that modification is less of a traffic-boosting strategy and more of a hygiene best practice. And in the process, Google rewards you with traffic, then great - but it is not a 'given.'
Honestly, I don't think we should pick a niche with the goal of getting traffic, so you can't say that content on business is not evergreen, while content on modern relationships is. The fundamental issue here is - it's not the niche, it's the format. So, if you are a website covering content in news format, the chances of it being evergreen are zero. But if you do long blogs or even opinion-based content, it will be evergreen. For example, Cosmopolitan has a section called Opinions - these are long-form content from the writer's perspective. But the same site also does movie reviews, which is only going to perform when the movie is being talked about online. So, it's not the niche that makes content evergreen - but the format you are working with.
Lastly, it's not AI vs humans - it's AI and humans. Collaboration over competition is the way forward. Google's content policies clearly talks about using AI to learn is fine but using it to create isn't good. I think AI tools has really helped us decrease the research time but when it comes to creating an original piece of content, it has to be done manually. The last update clearly proved it - the days of quick fixes are over.