Mozilla openly mentioned they might block network-wide methods to disable DoH and majority of people do not know that Mozilla (or Chrome etc.) are going to use their own settings, leading to unexpected behaviours.
How is that taking control away from a local sysadmin? It'd be a great thing if they did that, since then malicious network administrators won't be able to disable DoH on computers that aren't theirs anymore. If you're really trying to control devices that are yours, you'll still be able to turn it off via local Firefox policy.
There's a spectrum of options between "total lockdown of machines" and "nothing is controlled". Also, at least the way the announcement read at the time... it felt like someone forgot that there might be a need by local admin to disable it, in fact.
