Brave's Ads are optional (off-by default in the case of Ad Notifications), and matched-on device (so no user data leaves the machine). There is no conflict of interest here; Brave doesn't harvest user data. The Brave Rewards/Ads model is centered around _attention_, not data.
Regards to the "holding site operators and ad revenue hostage," I'm not sure to what you're referring. Perhaps the UI/UX of Brave Rewards ("Payments" at the time) in late 2018? If so, see https://news.ycombinator.com/item?id=31086397 what, I hope, will be a helpful answer.