Talking about a 6s pro and got at the beginning around 10 days without much GPS enabled exercise, after 6 years I get about 9 days!
Good thing with the Fenix line is that you stop the updates which I did a year in so I don't really care about them, but I do think they stopped firmware updates for the 6series about a year ago.
What kind of battery life did you have when you bought it, and how long is it now?
Does Garmin still upgrade the firmware?