One man's unnecessary noise is another's juicy tone and the reason for the extra feature. If you only do clean there's the other half? of the amps out there for you.
When an amp has a 'Gain' knob and a 'Level' knob at the front of the preamp the gain knob is essentially a tone knob that functions by increasing level and the level knob balances the total that goes onward.
A rule of thumb is to provide optimal signal through each stage by decreasing or increasing output to suit the following stage. So best is most often attained by giving a strong enough signal on to the preamp via the input gain.
Some preamps will give you more flavour by pushing them into overdrive if that's what you are into.
A too weak signal generally isn't going to spin your wheels. On the other hand I found a very pleasing tone in my Trace with an active EUB that sounded best when only just getting the light on.
So no hard and fast rules really.
The master output knob is usually a simple attenuation that you turn 'down' to get more volume ie less attenuation.
Some people just don't want to know it seems.
A P Deluxe has an 18v preamp that you can switch out for passive mode. Either mode lets you go 100% P pickup. The body is a little on the slim side.
P Deluxes cost about that new if you get a Spanish speaking one and tonally give you exactly what you are looking for, plus a whole lot of other tones you didn't ask for but they are free. Market served.
It's only a J when you engage the bridge pickup. Otherwise it's a P. Nobody cares what pickups are on your bass they only care that you sound right, if at all, but that's by the by if you only care what you sound like.
Could be worse if you had done the gig and gotten a case of covid. At least you got a nice country lane drive in with the fuel paid.
Back in the day I hitchhiked on England's country lanes. What a variety of folks I met. No whizzed of bass players though.
Many of the UK made Fenderesque P repro's come with J necks if you are that way inclined. Only problem is most are also fake road worn and the hardware genuinely rusted to hell.
Now you will feel the anguish of the bassist when a 'pianist' is playing (bass) keys all over you and perhaps be qualified to rectify your keys player, or maybe set to learning comping left hand chords your good self.