This folds in with the point
@superrific made.
If the national networks were to bypass the local affiliates with cable and streaming services and have those services access the national network broadcasts as opposed to offering local affiliate broadcasts, it would significantly damage local affiliates. Add in something like what you're describing with free DTC streams with ads or no ads for a small fee and I think you'd essentially crush the local affiliates.
My only concern with doing this is what happens to local news broadcasts. Local print news media is already pretty much dead and if local tv media were to follow, who reports on local issues and events, especially political ones? Who covers local elections or issues with government? Who covers local business issues or community events or significant problems in the community?
I don't know that local tv media do a good job of that now, but a mediocre job is better than no one providing those stories to the public.