I may have misunderstood the issue, but you can choose the DoH provider you want to use (Menu > Options > General > Network Seetings > Enable DNS over HTTPS > Custom).

Sure, a default has to be provided, but most of the people who will activate this option knows what they're doing, and which provider they want to use/avoid.

Firefox lets you change your default DoH provider and always has. People are just complaining Cloudflare is the default, not that it cannot be changed.

It hasn't asked me to, as you say, automatically use Cloudflare's DoH service. The default seems to have DoH disabled.

In OpenBSD DoH is disabled by default [1] :-)

[1] https://undeadly.org/cgi?action=article;sid=20190911113856

They are working on that and recently announced a partnership with nextDNS as a provider.