Earlier quoted context omitted.
DoH is intended to be indistinguishable from HTTPS traffic, if the application specifies a specific DoH server a DNS based ad block will not work. Right now The ad companies have not really figured this out and DoH largely works like port 53 DNS did. But give it a few years. They will up their game and our ability to mitm our own dns queries will vanish. I will miss it.
Freedom of DNS choice has nothing to do with DoH. And you can definitely mitm a non-configurable DoH resolver if you absolutely needed to do that, as long as you can add your own trusted CA on a device.
The attack vector that DoH offers is that data exfiltration companies will start shipping their own DNS resolver in javascript to work around DNS-based filtering. They can't do this with regular DNS because the network traffic can still be observed and blocked independently, but how will you block a browser from accessing specific https URLs without MITM'ing all traffic?
So yes, DoH does have something to do with DNS choice: it can completely subvert the OS-provided domain resolver service as well as the browser-configured one.