Before being able to successfully do a critical burst you must extend the damage stun threshold (critical stun state) until they are at high threshold. This is depicted by a red flashing "Critical Stun" under the opponent's life bar. It is purely damage that determines when you can do a critical burst.
In that regard, it wasn't a nerf in damage levels, but a nerf to the critical stun threshold levels. I forget the exact numbers but basically they added around 15 dmg to the threshold, which generally means another 1 or 2 atttacks depending on character. This provided a larger "middle" threshold for which it now took longer to get to Critical Burst. When you're hit in stun you take 50% of the base damage of the attack. So a Jab that does 10 damage does 5 damage when in stun.
This larger damage threshold allows for more opportunities for an opponent to escape the stun, and due to the other restrictions of the stun threshold it makes it difficult for some characters over others. Some only have one or two stun types that can put an opponent into an unholdable state, some have them but can't combo them together, and some still have them and are able to combo them together. (Talk about tiers...).
So because of the favorability of Stun > Launch due to the middle threshold, you'll rarely see players risk it to get to CB! levels. The CB! is rarely played because you can't guarantee combos into it (for most of the cast), and those that still succeed in doing Stun > Launch > Juggle it's more opportunistic then risking their CB! being held and instead just guessing the launcher. CB!s also aren't guaranteed on sit-down stuns as the opponent can stagger escape to guard them since they're generally 19-20 startup frames. So in the end you have a new feature of the game that its really only primary purposes is to "launch" for a Power Blow.
Only, the PB has been nerfed as well. Not only is it required for you to have 50% life or less in order to perform the PB, but you only get one if you do connect with it. So in general, you see people go for a launch after CB! even if they have a PB available because they're just so accustomed to "Launch and juggle". Honestly, it should be one of the two restrictions, not both (50% life or once per round).