100TB of Access Denied is only 38 MB/s, so not even a minor DDOS these days.

The difference is that serving Access Denied Leads to the users of these malicious browsers just getting more ads over time, as the filter lists can’t be updated anymore. Serving a special list containing popular sites would result in the users almost instantly not being able anymore to access these popular sites, resulting in requests to the developers to fix their shitty browser or switching altogether.

Blocking the browsers isn’t a solution because they likely fall back to being open, so the user doesn’t notice.

Instead, you need to break the user experience so they complain to the developer of the app, thus impacting reputation.

It’s unfortunate that the browsers developers are unresponsive and this circumstance limits the available options to easy list.