I 'need' a P bass because it works for me. Tone wise ive never been in a situation where someone else has asked me to use anything, or ive been in a situation where one bass doesnt work over another tone wise. What I find with a P is it's more plug and play. For me even a Jazz bass give's me more tone options to think about, and get distracted with. I do like Jazz basses, but I just find a P works in every situation, no fuss messing about with onboard EQ, and sits well in any mix. Tone wide open and thats it as far as that end of the signal chain goes.
I was put off for a while with the P bass chunky necks, but having found P basses with slimmer im happy to stick with it.