The Breath Meter should function differently. Going down, it's fine. However, when going up, it is quite realistic. Being a swimmer myself, when I surface from the water, I hesitate for a second, and then breathe in quickly. Translated into Minecraft, it would make sense if, upon surfacing, there is a small delay (half a second) and then your breath quickly replenishes. It's sort of a hybrid between the old and new system that in my opinion is more realistic and better.