So many good answers.
I don't think you have to have ridiculous theory to play jazz, or most styles cept'n classical... to generalize.
If you have great feel and ear inherently, you can be a fine bass player without gobs of theory. ... a modicum of theory understood well, coupled with great time and some greasy funk, you can do anything your heart drive you to do.
I play middle eastern (a little), West african and Cuban (because of my wife), jazz, funk, motown, punk, post hardcore math rock, nerdy progressive stuff... I love Fugazi and Shellac as much as Zappa and Monk.
I suck at rock and metal.
It's because my heart isn't there.
Because I grew up on country, I can play it... somehow that same upbringing I heard loads of 70s am soft rock and 80s hair metal too. My heart isn't in that stuff and I struggle to play it unless a particular song catches my fancy.
I wouldn't expect Megadeth and Testament fans to have any interest in learning Grateful Dead songs, or Bembe' (any variation).
Could they, of course, why not. But if you're hearts not on it then why would you expect it to be easy.
If you do a lot of sub work in various genres, you gain the skills of just picking up what's happening in on the spot and improving until you find solid points. That isn't snobbery or excess... that's jazz. The last last last thing I want to play are standards out of the real book. That's not jazz to me, cos it's played out.... like Aerosmith or Ted Nugent.
As with nearly every question on TB, there is a lot of room for "it depends."
Yes, jazz has a reputation for being a demanding genre that requires a high level of competency. It is also true that many great bass players in other genres tend to dabble in jazz a little; whether that is because it presents a challenge, or because it offer a lot room for people that love the bass, I don't know.
What I have noticed is that jazz runs the gamut from pretty simple bass lines to extraordinarily difficult bass lines. Not all of it requires demi-god like skills. Working around the genre does seem to require a very strong foundation in music theory, and the ability to interpret instructions or sheet music almost instantly.
However, I don't think that means if a person doesn't have a deep understanding jazz, or invests a lot of time in learning jazz, they are a "poor" bass player. There is a snobbery that follows jazz around like a bad smell that may endeavor to make non-jazz players feel inadequate. That doesn't mean it is true. There are a lot of terrific bass players that may have been able to play jazz, but they weren't known for it.
I feel like unless a genre of music speaks to you, you can't really be excellent at it. If you don't "get" jazz, you could have the technical skill to do it but none of the passion to make it believable.
I started playing with a jazz guitarist on and off several years ago, over the last 2 years we've gigged more steadily, not much money but a heck of a lot of fun doing jazz, R&B, roots, blues and some funk as a duo.
I've always wanted to play jazz but never really got around to studying theory academically. My theory is more practical, essentially from playing. The guitarist likes what I do, so do I and we've had nothing but compliments from audience members so I guess we're doing something right. Best part is I'm always learning something new.
When I read the OP, my first thought was my long standing OPINION that jazz musicians are to "musicians" what Ty Cobb was to baseball, what Bob Dylan is to writing lyrics, what Marlon Brando was to acting, or. . .. you get the idea. Jazz musicians are at the top of their game, and must be. They don't play "little boy chords." Is Walter Fagen a decent keyboardist? That man is so deeply rooted in jazz that he ought to have leaves growing off his fingernails.
To answer the question, "Does not being able to play Jazz=Being a poor bassist?" Is like asking "since I can't write like Shakespeare, does that mean that I suck as a writer?" Of course not! If you can't play jazz well, that means one thing: you can't play jazz well.
And not for nothing, but Jazz doesn't do it for me. Never has. I completely appreciate the degree of talent those men and women possess; but that music gives me no joy. Sort of like Carlos Santana. I know the man is probably to guitar what Neil Peart is to drums, but listening to him gives me absolutely no pleasure. Call me daft, you won't hurt my feelings.
Anyways, don't sell yourself short. If you can't play jazz, it has nothing to do, IMO, with the bigger picture question of "are you a decent musician?"
