no, jazz doesn't need a lot of theory. you just need the talent to be able to understand by ear.

mode scales just the name created by someone who want to be able to write down as a book, and teach as a written material. however a real jazzer will only play according to the "flow" of the harmony and apply the "melody line" that's appropriate.

jazz is about improvising, and is about "creating something" on the spot. which means, you're creating a melody on the spot, new harmony on the spot. in other words, melody have to be flowy, have to be nice, have to be make sense. if you think you can blah off with the notes within the whatever scale is jazz, then you won't be able to play jazz with soul. without being able to play with soul, you cannot move your audiences, heck you can't even touch you own heart with your own playing. this is a major flaw of the material taught in school.