My personal definition of turning an affiliate site into a brand is taking the affiliate income and:
Investing into diversifying the traffic sources (email, YouTube, Social, Paid etc) so you're less reliant on search engine traffic
Diversifying the monetisation sources so affiliate commissions are not your only source of income. Eg you invest into launching your own store with physical or digital products.
The space is definitely starting to mature and it’s going to get harder and harder to flip sites. Eventually the returns won’t be there.
You’re much better off building a brand, diversifying revenue streams, diversifying traffic sources, creating a community/email list if possible. aka building a real, defensible business…not just an affiliate scheme riding the current wave. I’m not familiar with a specific community around turning affil sites into something more, but the site indiehackers has a lot of cool stories about digital founders that may spark some ideas.