Flatwounds on P - what kind of sorcery is this?

I saw a used MiM Player P bass with EMG GZR pickups and Fender HiMass bridge for a nice price. I liked the sound when I tried it out but then time went by: brought it home, played around with sounds (amp and cab simulation) and to rehearsal. I was devastated that I found it sounds boring and lifeless compared to my Jazz bass.

Then I experimented with setups (action, pickup height), EQ, different playing styles: still nothing, just buyers remorse.

Then I tried different strings. Elixir roundwounds, Fender something standard roundwound. Still nothing, just remorse.

Before selling it off I thought I give flats a chance because folks on the internet are all over it. I am not.

I watched countless Youtube videos about it and I hated the thumpy-whumpy dead wood sound, so I ordered a Fender 9050 roundwound flatwound because it sounded like a brighter flatwound.

I put it on the bass, thinking why am I doing this to myself and just be happy with my Jazz.

Plugged it in and I was completely shocked. The damn bass came to life with mid heavy, growling pure bliss. Everything is balanced, no fret noise, no finger noise and still has enough highs.

I can't stop playing the damn thing now!

What on earth going on here?