I agree with most of your points, however I think the cons outweigh the pros.
An embedded or IoT device might use DoH to bypass your network settings and communicate with its home server. It doesn't need to ask your router "where can I find this address?" And you have absolutely no control over it.
- Smart TVs
- Smart toasters
- Smart thermostats
- Applications on your phone
- Proprietary apps on your computer
If they implement their own DoH, you have lost control over your devices. The only remedy is to block internet access for those devices/applications and then they basically lose whatever "smart" functionality they had.
And that's probably not a bad thing.
Now, for me--as someone who knows better than to connect "smart" devices up in my home--this is much less of an issue. But for someone who doesn't know better, the privacy implications here are far more concerning. Even if they don't know how to add a Pihole to thei network. Even if they don't better than to have "smart gadgets" in their home... the loss of the end user's ability to administer their network is dangerous. It's yet another step in the wrong direction.