I have long been using my own recursive DNS server through Wireguard on my GrapheneOS device. I don't see how using DoH through one of the few well known centralized providers is better for privacy.

Any domain could instrument their DNS to associate your DNS servers with your sessions which is highly unique for you and possibly connects your otherwise distributed devices, it would be odd to me if none of them try to add this to a profile for you just with the expectation of clustering users by more typical configurations.