Just because it is not the advice that is expected does not make it bad advice. Obviously these names have some questionable behaviours but in this case they often have separate privacy policies for their DNS services (or the Mozilla endpoint for their DNS services) which makes it much better than the other Google products which are lumped behind a single privacy policy which isn't very privacy friendly.
Unfortunately it is impossible to know for sure they are complying with the privacy policy, but this applies to all providers, no matter how large or what businesses they have other than providing DNS. So while you shouldn't blindly follow some random post on the internet you should may give these providers a second look-over and consider that these large companies have some privacy benefits if their privacy policy is accurate.