Like any other tool, it all boils down to personal preference. That said, someone who works with their bass every day to earn their daily bread is not going to pick up some iffy jankboat and depend on it to make a living any more than some kid just starting out is going to get a 10K coffee table custom to learn Smoke On The Water.
Since it is personal preference, it often comes down to what the players fiscal situation is rather than their actual need or what they would love to have if they could afford it. I've seen some very serious pros using middle of the road to even low endy basses and I've seen people who just learned Smoke On The Water with basses in the stupid expensive region of bassdom.
Another thing that I think figures in is a lot of players, and I used to be one of them, refuse to accept that it's them and not the bass, so they burn through a ton of different types, makes. variations, etc, looking for "the one". What I eventually learned when I finally found "the one" was while it addressed every desire I'd ever had regards play-ability, variety of tone, color, finish, and on and on, it was still my hands choking out the final product of our collaboration, and while I could now get tones I'd always been hearing in my head, it didn't make me a bit faster, or more accomplished. To that end it did help because I wanted to hold it more and play it more, and learn more. That lasted until the novelty wore off, and while it was my only bass for many years, the minute I had even a shaky justification to get another one I didn't bat an eye, I went and got one.
These days "the one" spends most of it's time cased and I've dropped any illusion of ever being anything more that what I am. I didn't put in the time to be anything else so rather than be frustrated or look for other things to blame for my place in the bass players food chain, I am content to be what I am and enjoy what it brings me. Somewhere along the way I also came to realize that a well set up Fender jazz may not be "the one" but it's potential far exceeds my ability to coax said potential from it, making it plenty good for what I am capable of, and thanks to modern manufacturing methods and the realities of our global economy, a real whippersnapper of an example of a Fender Jazz is also within reach of most any player's budget. Like anything else you can get silly and spend a crap ton on the high end sig models or clones and they will have a few little trinkets that set them apart and will always bring a "wow" when displayed in public, but a decent little made in Mexico J bass with a good setup and some decent pups, will serve all but the most discriminating players, and of course those who feel that even acknowledging the existence of Fender makes them somehow less unique.
But that's one of the many joys of life in this great country of ours. We are free to be as practical or as silly as we want and as long as we are not pushing our fun uninvited into someone else's fun, it's all good.