Among other things, NextDNS use the publicly available openphish database and that's why it got a high score it seems.
At the moment, almost all the free feed openphish sites are also blocked by Google Safe Browsing (Tested in Firefrox).
As @SeriousHoax mentioned in Firefox, and I think Chrome too, the list is already part of Google Safe Browsing feature. I have no idea in full or partially, however. Having that said, there is a built-in list within uBlock Origin called 'Phishing URL Blocklist' under the category of malware domains. Which is a list made up off OpenPhish and PhishTank. It's only disabled by Default! So technically by enabling that one list you render this test less effective, but this is assuming the tester used the non-paid feeds!