I am talking about the fact that the ARD itself is the collective group of all regional broadcasters (look up the name) and any programme is produced either by one of the regional broadcasters or by the shared production company Degeto. And of course is also shown in the "thirds". Take "Rote Rosen" (with questionable quality) and you will see it is also shown on rbb, hr, NDR and MDR.
The organisational structure causes what you can watch where and I am arguing that garbage produced by the "Thirds" is not only dumped to Das Erste but shown elsewhere as well. You gave me the current programme, I gave you "Rote Rosen" but that did not convince you. Here is more: "Sturm der Liebe" shown on BR, hr, MDR, NDR and rbb, "Bristant" shown on MDR, "WaPo Bodensee" shown on SWR, hr, NDR and BR … that is not "pretty much nothing".
Take a look at the first column of https://www.tvinfo.de/tv-programm/ard
Pretty much nothing in there is also shown at any third programme. The programmes are almost completely distinct.
Evening news are actually the one part where the third programmes show the same as the ARD.