> Because the AGPL (and even general GPL) are copyright licenses, they simply do not have anything to say about software that is distributed separately

Of course they can. The nature of any software license boils down to "this work is protected by copyright. If you comply to A, B and C, you can do D, E and F that otherwise would have violated copyright law". A, B and C can be whatever you want. It can be "don't use this in nuclear power plants" (MS likes that condition), it can be "if you make less than $100k anually" (Unity etc), or it can be "if you share the source code" (copyleft). You can make that clause as wide or unrelated as you want

The real issue with GPL and AGPL is how badly defined the boundary is unless you have a single compiled C program