I've certainly seen this reduction of the organic search 'real estate' for my SEO clients, especially over the last 3-4 years.
There is one caveat, however:
While Google is trying to own the big volume search queries, there is still plenty of opportunity for the rest of us to capture significant organic search traffic from long tail queries.
Answering audience questions, addressing objections, fears, anxieties, motivations, etc. with your organic content is still a great way to generate traffic via SEO.
That said, I think you're spot on about owning your audience once they come to you- i.e. adding them to your mailing list and then strategically tiering your content so that you can earn directly from the premium, paywall content.