I agree with OP. Find my friends and other apps like health, stocks, watch, etc should not be integrated into the OS but rather be offered as a downloadable option. Remember the infamous Newstand app?
Just like the apple apps imovie, Pages, Keynote, Garageband, etc, Find my Friends and the other apps mentioned above should be designed like that.
GarageBand, iMovie, Pages, Keynote and so on are apps, creative and utility. Things like Health and Find My Friends are iOS features. So no, they shouldn't be standalone downloads.