This is exactly correct. The purpose of DoH is two-fold; for Google, to allow themselves to be the endpoint DNS resolver so they can both bypass local ad blocking and collect statistical behavioral data (I am aware that their policy does not permit them to do this; it will certainly not be the first time Google violates their stated policies in the mission of serving advertisements), and for e.g. Cloudflare, to centralize and control additional pieces of previously-distributed Internet infrastructure (and thus permit centralized monitoring not if but when they are compelled or subverted by the intelligence community).

Mozilla I don't understand. The most likely explanation appears to be that they are still in a catch-up-to-Chrome mindset, which is a disservice to themselves and their community.

DNS queries should be encrypted. Centralization-by-default is not the answer and people should look more closely at the incentives in play by those pushing the DoH standard. I appreciate the efforts of e.g. OpenBSD to prevent this side-channel leakage of user data to private corporations: https://undeadly.org/cgi?action=article;sid=20190911113856