That’s an interesting observation.

The person doing these tests works for Brave and doesn’t disclose this on the main page. He keeps spamming social media with his results and therefore this comes up time and time again. The main problem is that he refuses to test browsers which have been configured, he always tests them ootb. For Vivaldi this means ad and tracking protection is disabled, even though the choice of setting this up is presented to the user in the very first setup steps (one‐click operation), without the need to visit settings …

I wouldn’t take the results serious. If you want a sliver/the chance of privacy, you have to use Tor browser anyway.