7 years updates plus 2 battery swaps will take a flagship phone right to the edge of how long you’d want to use it anyway.

I think, 7 years would be amazing, but also good enough. Or to put it differently, after 7 years you get into heavy diminishing returns, since almost all users will be moving on/have severely broken their phone before that.

I’ve had most of my phones until they where 5-6 years old (I used to buy used, so I had older phones even though I didn’t have them for quite that long). After that time, they usually fall apart anyway. (Two of my phones developed frequent random reboots around that time, one wore through the cable connecting both halves of the slider, and one killed died when I tried replacing the battery and accidentally cut through the screen cable).