That's actually a pretty gross oversimplification of the system. I'm simplifying a bit myself here, but for the most part KI combos are comprised of an opener, certain specials and normals linked back and forth, then an ender. The normals in the middle are usually auto-doubles, which is just pressing an attack button during the special linker and automatically getting 2 moves of the corresponding strength to follow. On defense, there's a different breaker for light, medium and heavy attacks. Obviously, the time to react and damage both scale up with the strength of the button.
Back on the offensive side, there are also manuals, which have stricter timing (similar to links in other FGs) and only hit once. They do less damage, but also give the opponent less time to react and can be used to bait out people that would otherwise be hitting their combo breaker on the second hit.
Between lockouts and counter breakers, it's still risky to go for a combo breaker if you do have some sort of read, because the damage you take while locked out is going to be entirely heavies, which is when you start to see the absurd 50-70% damage combos in that game.
So I mean, breaking lights/mediums is still usually a guess but there are certainly players who will react to heavies and certainly educated guesses you can make based on player habits. I don't really like the mechanic myself, but the risk/reward for someone who's just guessing is heavily stacked in favor of avoiding breakers altogether. Good players will rarely guess break unless the combo is likely to kill them anyway. TACs they are not.