This was only the case in this experiment. From the article:
> We’re also working on privacy preserving ways of dividing the DNS transactions between a set of providers, and/or partnering with servers geographically.
That is still less different providers than can currently be used, so it is something that we should be concerned with long-term, but I don't think, it makes sense to throw the technology away. Just be concerned that there are the right kind of providers used for this.
I figure, this is become like the CA infrastructure, for better or for worse.
If I had to guess, they will likely have a heuristic where your local DNS is first checked somewhat regularly if it supports DoH, if not use the one configured in Firefox, if DoH is enabled that is.
The more important question is who we trust though. Currently, the DNS information where we go on the web is spread across a number of national internet service providers. In some countries, they feed this info to the NSA. In others, they may not.
This new DNS system makes everybody use a single DNS endpoint, the same one across the world located in the US.
Is this better or worse? Depends on your isp and country.