This is a pretty normal request. The producer knows the bass they have. He knows it's set up perfect and that there are no electronic issues with it. As much as I hate to say it, if this producer is as big of a deal as you say he is you're lucky he's even letting you play on the recordings at all. It's not uncommon for a producer to bring in a session drummer, bassist, and rhythm guitarist. He knows what his session musicians are capable of and that they won't waste his time.
Actually, no it isn't.
Telling the artist to leave their instrument at home.
And no it isn't set up perfectly. Might be electronically sound, but set up perfectly for who exactly?
A P-Bass with high action and flats is so far from perfect set up for me it's pathetic.
And also, if you're footing the bill, and the producer wanted to use someone else, then, well, fire the producer.
Again, we didn't get any clarification as to the whole deal here.
Who's paying? Simple.
If you're paying, you can do what the hell you want and it's his/her job to be there as long as it takes.
I've worked on a number of sessions with my own groups and as a hired player.
Maybe it's just me, but not once have I ever been told not to bring my own bass.
I've played on national commercials and had tracks on movie soundtracks.
Always used my own bass.
Again, if a producer doesn't know how to make you feel completely at ease, and completely confident in what you are trying to do, then they really don't have any business telling anyone what to play.
It's their job to get the best performance from you that they can.
I've never heard of being told to leave it at home. That's absurd IMO.
Who knows if what you have is better than what they have. And they should know that.
I need to be a little clear.......My goal for the last 10 years or so is to be as generic sounding as I can. So I can walk in and "fit" into any situation.
I usually bring my old Jazz, my 65 Hofner and a Sadowsky 5 to any session I do. So I usually don't have any issues really.