I think that statement is too bold.
It's simply a personal preference, depending on the scenario which applies to you. I have the VPN DNS-servers set to Disabled, because I specifically [B}not[/B] want them to be used. I'm using the NextDNS CLI Client and have a ProtonVPN subscription. NextDNS provides parental controls, logging, black- and whitelisting, broad insights in how my kid uses his Internet, regardless whether he's at home or at school. At home he's connected through the tunnel of the router, when on his way, as soon as he gets out of range of our trusted wifi networks, an app called Passepartout (which allow custom DNS server) immediately rebuilds a connection to ProtonVPN. That way I feel a lot safer. So, in my case, I specifically prefer to use another DNS than my VPN-provider provides. Not only are they slower, they also lack the many possibilities NextDNS offers me. So it's all a personal preference, based on what you want to achieve.