I agree that composition is the core idea and I was disappointed that the author neglected to summarize the idea correctly. Composition is a structured way of describing a unique task using a few common nouns and verbs.
But composition needs to be understandable and controllable to be useful.
For it to be understandable, it needs to match the user’s anticipated mental model. Now, this isn’t an appeal to an intuitive notion uninformed by user education. But it does need to make logical sense to connect two things together temporarily to solve one task. And that logic needs to come from the user and not the developer. In other words, the developer needs to provide concepts that conform to a user’s algebra. For a photo editor, that’s hard to provide to the average user. For some CLI tools like wc and cat, it is easy.
For composition to be controllable, the primary method of configuration needs to be in the contextual relationships among the tools and not in the tools themselves. That is, using cat and wc to count the number of words in a text file is primarily enabled by the filesystem and shell features, none of which require user configuration during the operation. Configuring wc to count instead the number of lines doesn’t distract too much, but imagine counting the number of lines emitted from a streaming serial device: you want it unbuffered, but only kinda because of other issues that arise, like multiline error conditions. In that case, the value is disrupted by edge cases and you have to configure the nouns (the serial stream at least) by looking it up on Stack Overflow. It’s not just easier to consider building a monolithic tool, but arguably the right thing to do because you need to configure everything so much. Plus, this is too much to expect the user to handle through a simple composition.
In my opinion, desktop composition doesn’t work because the tasks are often beyond the limits of composition. And without a culture of composition among users, it’s harder and harder for remaining desktop applications to do it. Especially as younger users are unfamiliar with concepts like the filesystem, system keyboard shortcuts, “saving” files, offline operation (i.e. you have to reason through a problem and cannot lookup the answer), etc. Better to go with the monolithic app model, which can still use plugins under the hood or multiple processes for developer productivity. And I’m sad about that.