I'm glad you know better than the last producer/engineer that I worked with considering he recently recorded a record that made it into the Billboard Top 20, and has had stuff featured in an Oscar award winning film.
Maybe you could email him with some advice.
Realisticly. Less than 5 minutes to get my P bass sound dialed in.
well, that's fine, but I never claimed to know better. what I mean to say is that I doubt very much that the setup time is going to be a whole lot different on any resonable bass.
I expect that the reason why some engineers request people use a fender is mostly just a precaution to prevent them bringing in some weird hacked up "custom" thing which may have some issues that would interfere with doing a decent recording.
And probably some of them just buy into the same marketing and herd mentality as the rest of us.