A couple things (even if they've been said before)....
1. Hard bop is not the only genre of jazz. This should be something that is obvious and self-explanatory, and hopefully evident to electric bass players (this is an electric bass forum after all), but there are still a good number of people on this forum that come by that seem to think that blowing over Moments Notice is the only way to play jazz. There is jazz music before 1960 and, more importantly, there is jazz music after 1960. There is also a wide variety of styles, ensembles, variants and fusions of jazz. Hard Bop is great, but the Wynton Marsalis neoclassical revival in late 1980's forever ingrained it in the heads of up-and-coming jazz students that Hard Bop is the only way to go, and it forever shall be.
2. Jazz music does not have to be improvised in order to be jazz. I don't believe many people would disagree that the music of Duke Ellington, Thad Wilson and Count Basie was jazz (incidentally, Duke Ellington hated being called a jazz composer). A Tone Parallel to Harlem is 14 minutes long, and every single note is written out for all the musicians, is it not jazz? The tune "Lush Life" by Billy Strayhorn never is played with improvised choruses, is it not jazz? Improvisation is a vital part of jazz music, but it's not what makes jazz jazz.
3. Reading is part of the jazz scene's culture. Even if you're playing relatively conservative hard bop in clubs night after night, there will always be an instance where you'll need to read down a chart without rehearsal. Nobody will give a crap if you can listen to it once and then have it down cold, if it's not out on the first go around, you haven't done your job. Reading music is an auxiliary skill to the actual performance, but vital just the same.
4. The skills necessary for large jazz ensemble performance are virtually never improvisation beyond the ability to comp to chord changes, and even then for high school level and some college level, not even that. Reading and the technical ability to perform what's on the page in terms of notes, dynamics, blending, etc are what you need to worry about, not improv.