it is interesting. I don't get exhaustion because I don't talk to the assistants that much, but people talk to their virtual assistants in a different cadence or register. Instead of "alexacanyoutellmethetime?" it is "ALEXA...WHAT...TIME...IS...IT."
Owning an Alphabet Corp Branded Espionage Hockey Puck (tm) myself, I must admit I'm fairly impressed at how far voice recognition and natural language processing has come, despite this. I remember when you really had to talk in that stilted, properly pronounced, methodical way, and then tentatively wait for a response for what seemed an age -- and it wasn't that long ago (maybe like, four or five years?). Nowadays, I can vaguely mumble at mine from the other room without thinking too much about sentence structure or how I'm pronouncing words or the volume or speed of my dictation or switching off things making background noise, and it usually does the right thing, and responds about as quickly as a person. It definitely feels a lot less mentally draining!