Who would you want fixing your plumbing? A plumber or someone who pretends to plumb? While the difference don't mean much to you, there are people out there that use Illustrator and never touch Photoshop, because Photoshop doesn't do the types of things they require. And this isn't about adding some more features to Photoshop. This is about the fundamental, bedrock differences in the types of technology we are dealing with.
Maybe, one day in the future when computer technology has moved away from digital, pixel based art, the lines will blur enough that we can finally merge the two (or maybe three) applications together. Then there could be just one place to go for all creative, artistic endeavors.
Lets try another analogy. You are asking that all artists that may use one of three media, lets say Photography, oil paints, and a typewriter, to just use one that has extra features that make it seem like it can do the work of all three. Maybe a camera that has a way of blurring the capture to make it more painterly and an option to add text to the image as well. While this might cover some workflows, there would be those who use oils and produce things that no camera ever could, and especially no typewriter.
But the way you've been describing things so far, it sounds like Photoshop already does everything you could ask for. Why do you go into Illustrator and InDesign sometimes?
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