The TTK can feel sort of long. What makes it feel very long for me is this whole "down" state. I tend to "down" 2 players in a single firefight but never get an actual kill because I didnt finish them off.
Its like we all have about 300 total hit points (not hp as in life). 100 off the shield, 100 off the health, and then there is down state, which feels like 50 health.
50 health and with the possibility of another 100 hit point down shield. Sure sounds like a long Time To Kill if you go over those numbers.
I personally think there should not be a down shield and that the body shield should be used in all states - down or not.