The P6 is so much more synth. Don’t really understand the design-choice for a mono output. Love the filter settings and improved ui-design though.
I spent more than a few early months using only one output of my P6, eschewing the internal FX, and running the synth into an ancient chorus pedal. All in the spirit of "trying to make the P6 sound like a P5." I gradually made my way back to the stereo outs and internal effects of the P6, as I learned to love the synth as very much its own entity. I'm delighted to see a mono out, no fx, no sequencer/arp etc. on the new P5. The Fatar keybed and MIDI/USB are the sort of "modenr" features I'd expect, but I love that Dave has basically just made a new, "best of all worlds" Prophet 5. The P5 has such weight and majesty to its sound, and always sits easy in a mix for me. It's pretty self-contained in the best way.
I've truly fallen in love with the P6, and have said before that if I was to pick a single synth to use for everything, it'd be that one. I now own two P6s and have a rev 3 P5, but there's simply no way I can shake off the idea of "needing" a rev 4. The Prophet 5 has always been the ultimate synth to me.