Each instrument isn't its own medium, and none of the articles you link argue that. That's all I'm saying.
But each instrument can produce its own medium ("Trumpet Music", "Cello Music", "A cappella Music"); at least they are if we apply McLuhan, who, to my knowledge, coined the common usage of the term; if I miss something here, please tell me! The articles that I linked of course don't say that every kind of instrument produces its own medium, since I brought them up as a reaction to your claim "that only the distribution is considered as a medium". The other part of my post should help to understand what I meant, though :).
Like how each image editor isn't its own medium.
The editor not, but the images produced by it might be one specific to this editor!
An editor that creates a very unique style might be considered to produce its own medium; other cases include tools that are in the focus of the public debate ("Photoshopped Images" might be considered as a own medium if we regard a niche of images as such, and if they are discussed as such!). I tried to give various examples for the ambiguity of making something a medium earlier in this thread.
To link this back to the OP:
All of this certainly often applies to "AI images", that have often very distinct features that make them recognizable, and that are a product of a hotly debated technology; making them - if I'm not mistaken - clearly a medium of their own (that does, however, at the same time belong to a wider category of media and might be included and transformed into other media! An example for this is a banner featuring an AI generated image - both the banner and the image depicted are a medium).