"I want a single source for my DNS."
I don't like applications that do their own DNS resolution. I use a text-only browser that relies on the OS to do DNS resolution.
But imagine your DNS is filtered. Would you still want only a single source, e.g., your ISP? In that case, wouldn't you want multiple sources?
When in a DNS-filtered environment, e.g., a hotel, DOH outside the browser can actually be useful. For example, I can retrieve all the DNS data for all the domains on HN in a matter of minutes using HTTP/1.1 pipelining from a variety of DOH providers. The data goes into a custom zone file served from an authoritative nameserver on the local network. Browsing HN is much faster and more reliable when I do not need to do recursive DNS queries to remote servers. The third party resolver cache concept is still really popular, but IME most IP addresses are long-lived/static and "TTL" is irrelevant. I rarely need to update the existing RRs in the zone files I create and the number that need to be updated is very small.
DOH servers are not the only alternative source of DNS data.
Ideally, I prefer to avoid third party DNS altogether. Nor do I even need to run a local cache. I wrote some utilities that gather DNS data "non-recursively", querying only authoritative nameservers and never setting the RD bit. It is very fast. The only true "single source" of DNS data is the zone file for the particular RR at the designated authoritative nameserver(s). Everone else is a middleman.
I am not a fan of applications doing their own DNS resolution, even if they use DOH. But I have found the existance of DOH servers, i.e., third party DNS caches served over HTTP, can be useful.