It absolutely both blocks (many) pre-existing ads and places its own ads. Those are both overt features of the browser.
> If a user opts-in to Brave's ad ecosystem, then they've also made a decision about what content funding model they want to support.
It's not really a content funding model, since whether Brave shows (and derives revenue) for ads or not (and whether it blocks the ads the content supplier has decided to place or not) has nothing to do with any agreement or payment to the content source; it's a browser funding model.
The content funding model it (indirectly) promotes is the covert “organic” advertising model, where rather than being separated and distinguished from the editorial content, the promotional content is integrated with and inseperable from the organic content.