I felt I had to share this as it surprised me:
I have a sire P5 with TI flats and just bought a fender American pro 2 precision bass which I put TI round wounds on. Both are 4 string.
I was struggling with the sound on the fender + rounds a bit weak and just not there. I read how people don’t like the V2 pups on this bass and was considering returning it.
But then I swapped the strings and put the TI flats on the fender. Immediately I was blown away there was that classic p bass growl the difference was amazing. It seems these pups are more suited to this tone. Conversely I put the TI round wounds on the sire P5 and they sounded great with the more modern tone. It seems the P5 pups work well with both strings. But the fender pups prefer the flat TIs. I wish you could get the TI flats as low tension as the rounds as I prefer the ease of playing on the rounds.