The bass line seems pretty straightforward to me ... both rhythmically and harmonically. I can't understand what his problem with your part could be. Maybe he should independently work on his guitar and singing parts some more prior to the next stab at it.
I'd more or less agree with this, but it isn't a bass line that's going to lead someone clearly through the chords.
To my ear it sounds like, if you have a stripped-down instrumentation, you'd probably do well to play the same rhythms (such as they are) but outline the chords more explicitly. We all know that the cats Jamerson was playing with would have nailed the tune if he'd come in playing like Ornette Coleman; but to make the tune sound good with the army you actually have, some modification is likely to be helpful.
I wouldn't consider this an "exotic" or "rare" tune, but I can see how the changes might need clear outlining for a vocalist.
You also don't know what kind of scratch track the vocalist on the recording was singing with. He may just as well have been hearing the piano playing a bunch of root position chords the whole way through.
I for one don't believe groups should be forbidden from performing tunes unless they can "do it like the record". "THEEEE RECOORRRRRD" was probably assembled over the course of an 8 hour session from multiple tracks, bringing musicians in and out for even a few bars as needed. There may very well have been 20 people on that one track, some even overdubbing themselves (like how you make a string orchestra out of one violin and one cello player). So now you take OP's four piece, guitar, bass, drums, keys, and say "play this tune". It's simply nutty to insist that they reproduce the recording. I played for many years in a five piece (guitar, bass, drums, sax, vocal) and we did tunes from the whole range of classic rock and R&B. If there was a whole brass section there, I had to do what I could to reproduce that feeling on one saxophone. If there were two guitars, the one guitarist had to do the best he could to reproduce that feeling with one guitar. Prominent keyboard part? We'd divide it up. I don't believe we EVER not once had an audience member, booker, or other say to us that we "weren't playing it like the record". We did get criticisms, mostly for things that were valid, but that was not one of them.