I was able to fix the stuttering dimming by modifying the transition time in @drinfernoo’s super helpful blueprint (Thanks!). The key is to multiply the transition time by 10. Maybe this really should be fixed in the converter at zigbee-herdsman-converters/lutron.js at f14c9065d4f517549f5e213e3ee7cc3787ce0c57 · Koenkk/zigbee-herdsman-converters · GitHub, but you can fix it locally by updating the blueprint transition time like this:
transition_time: '{{ attrs["action_transition_time"] * 10 }}'
With the change, I’m getting dimming as smooth as when the dimmer was paired with my Hue hub. The smoothness is working for Hue bulbs, but not for my Lutron Caseta dimmers.
Update: I can smooth out the Caseta dimmers by going to a factor of 50, but not surprisingly that introduces significant lag.