I'm not using StreamDeck+, but Loupedeck Live which is a very similar kit (6 rotating knobs + 12 touch buttons and some more).
I originally also used keyboard mappings, but found it quite cumbersome to set all those up in X-plane, and was also not entirely happy with the speed of the rotary knobs (too slow for some commands and too fast for some others).
Then learned about XMidiCtrl, which is essentially a MIDI Controller interface into X-Plane. https://forums.x-plane.org/index.php?/files/file/76419-xmidictrl-a-midi-controller-plugin-for-x-plane/
It takes a bit of setting up (mainly on Loupedeck side, StreamDeck may be easier here) as well but I find it more flexible its use and it has solved the speed/lag issues with the knobs for me. It comes with an example file for the CL650 out of the box, but I have created a more expanded one that covers all FCP/DCP/CCP + baro controls.
It works really well (also in XP12) - happy to share if helpful.
Marc