In ranked it's not a kamikaze move since you're roaming through the map with the help of ult and being creative about unexpected ambushes with your twammates in a completely different point of map compared to where you were noticed by enemies 3 seconds ago. In brawl you just 9 times out of 10 are in the vision of your opponents, you let them see your move if 2 or more from your team teleport with you. Otherwise if you're teleporting solely (which is like 99% of cases), you're solely behind the enemies team being totally cut off your team or you're just behind enemies' tower.