I think I probably would disagree. At a certain level, and in certain industries, there is a high degree of bleed between different kinds of work - especially for video production or complex image manipulation. When Adobe dismantles products into multiple apps, some functionality tends to be duplicated across them, which then introduces its own set of issues (i.e., look at Premiere, After Effects, and Speedgrade, and the ways in which all three of these products can be used, in different ways, for colour grading, or the ways in which certain functionality ends up moving between Premiere and AE in subsequent generations).

The idea that applications are necessarily faster and more stable if their codebase is smaller isn't necessarily the case, especially if the alternative is moving files continuously across multiple separate applications, requiring intermediary tools (like Dynamic Link) to facilitate those transfers. Perhaps Sketch is a better tool for your workflow, and i think that's fine, but I'd imagine many PS users move across different kinds of functionality, and would much prefer to deal with a single interface for this instead of managing multiple smaller applications.