I definitely agree that it is and feels like an “instrument”.
Absolutely. It's definitely geared toward immediacy and playability.
To me it is what the Kurzweil K-series was trying to be.
Perhaps from a performance control standpoint, but definitely not from an editing point of view. If anything, I'd say it's the complete opposite. The Prophet X sacrifices depth for simplicity at every turn where VAST and KDFX lean into complexity to give as much control as possible, and that has both benefits and drawbacks.
The Prophet X model makes it incredibly easy to experiment, even to the extent of making changing a patch part of your performance. That's hugely valuable and a part of what drew me to the instrument as a marked contrast to my Forte. On the other hand, lacking the flexibility to have distinct key ranges with their own envelopes, filtering, and effects makes the Prophet X ill-suited to purposes for which my Kurzweil is perfect. Drum kits leap to mind as a prime example. Something as simple as having hi hat samples cut one another off while playing alongside other drums isn't well accommodated, nor is deciding to mix and match drums from multiple factory kits.
Ultimately, they're very different designs, though I do find that both have a special sonic appeal that I can see fitting into the same conceptual bucket.