I have two “old” GE/Jasco Zwave switches (12730) installed for awhile now and am generally happy with their performance with Google assistant with the exception of having to use shortcuts for each fan for ‘low’, ‘medium’, and ‘high’. And also Google had broken functionality so that saying turn off “x” lights would also turn off my fan as well despite not having the name light. That is fixed as of a day or so ago thankfully.
But I was wondering if there was any leverage in using a custom device handler to report to Assistant that the switch is actually a 3 speed (plus off) fan and not a dimmer as it shows itself as. There seems to be some support for that with actions for assistant ( https://developers.google.com/actions/smarthome/guides/fan )?