I can't really consider that a comeback mechanic. Keep in mind that if you're down two rounds, get the meter boost, and use it mount a 2-round comeback, THEY get a free meter at that point too. Both players get full and equal use of it, unlike X-factor or Ultras which may add a one-sided advantage due to the ridiculous buff in the case of X-factor and the fact that round-ending removes the other player's ultra meter, where they may have ate their comeback boost and now they can't send it back at them.
As far as throw breaks doing damage... keep in mind it's just a sliver of health. It's just right for landing a throw attempt which already requires a correct guess. The way it is now, the thrower has a big disadvantage. They must guess right twice in order to do any damage, and the defender only has to guess right once. Also, the thrower has to close distance if players are spacing properly so really, they have to guess that an attack isn't coming before they can enter into that guessing game.
Say the thrower manages to get in. Defender can either duck while reacting to block slow lows and mids, or stand and throw break. Thrower can either throw or do an unreactable mid. Throw's expected damage on successful attempt will be close to the average of the throws divided by two, usually around 30 up to 45 damage. A safe unreactable mid will generally be somewhere between 30 and 65, matchup specific on safety and damage. Unsafe, again, matchup specific, 55 to 80. So the mixup is 30-45/30-65 against good punishers, else it's 30-45/55-80.
Assuming the defender is rooted in place, the minimal defense, (but not long enough to get side-grabbed,) the reverse mixup can be as strong as their duck-throw-punish (not that high) and their mid punish. Against certain characters, it's just not in the attacker's favor to mix up on them. Sophie, for example, can easily duck punish with FC1B8BAK (76) if the player is deliberate about the throw guess, and can punish hard enough to deter use of unsafe mids. Tech crouches in general are really good, so often it's something like 30-75/0.
This doesn't take into account more advanced offense and defense and the fact that the defender first has to get in... but the offense should be favored a bit more.