Learning improvisation will require you to employ a system that allows you to compartmentalize and categorize the sounds (tools) you want to employ in your storytelling. Whether you study traditional theory, develop your own theory or use some of both, you are going to have to put a system of categorization in place.
No, you don't have to study "Dorian" mode (or any kind of formal theory) if you don't want to, but why WOULDN'T you if the rest of the world has already placed a label on that sound? If you did then you can at least communicate effectively in English with like-minded musicians and even get second opinions on the matter.
Too often, I hear I hear people say to me, "Well John Doe doesn't know any theory." I first respond by saying, "Well, you're not John Doe! And I am certain he has a system in place to where he knows where the appropriate sounds are on his instrument."
Playing solos isn't hard, inspired improvisation is. If you don't endeavor to use every tool possible to cultivate your creativity then just go out and join a "fun" band and copy a few solos and riffs and just recycle them at will.
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