I'd been thinking the 21012 was more J-friendly than P-friendly. Well tonight I finally got around to trying it with a real P-bass instead of a P/J, and hoo boy what a difference. My P-bass has never sounded better.
If I had to compare, it feels a lot like playing thru a 210 + 115 stack. But this is so much better tonewise and with matching drivers in the same box.
Earlier I posted about the 10s being bright and I still think that's true. But they work well for a P with flats and alnico pickup. I even used the tweeter, hahah! It's all there, clarity, punch, definition, great high mids and deep lows, and most importantly wood. I'm blown away.