Bump for some math.
Now, Rib Cracker doesn't just do damage, it's also a debuff. It does -Damage and -Resistance (the former of which I didn't even know about, which, considering I've played two StJ Brutes to 50, should tell you how effective it is). The -Resistance is 7.5% and lasts for 5 seconds, so let's calculate how much damage it could add.
Suppose on a Scrapper you land Rib Cracker on a target, and then follow it up with the three strongest attacks you can land in the 5-second debuff window, which would be Crushing Uppercut, Shin Breaker and Sweeping Cross (maybe*). Crushing Uppercut is used at combo level 3, and all three follow-up attacks also miraculously get critical hits. The extra damage from Rib Cracker would be as follows:
Crushing Uppercut: (3.975 + 3.18) * 0.075 = 0.536625
Shin Breaker: (1.64 * 2) * 0.075 = 0.246
Sweeping Cross: (1.575 + 1.5) * 0.075 = 0.230625
Rib Cracker itself does scale 1.32 damage, so the total damage from Rib Cracker and the extra damage its debuff provides is 1.32 + 0.536625 + 0.246 + 0.230625 = 2.33325. Meanwhile, Assassin's Strike outside of Hidden with no critical does scale 2.5 damage. In other words, StJ Scrappers using Rib Cracker with the most ideal circumstances will still do less damage than StJ Stalkers will at the baseline. To be clear, I'm not posting this because I want StJ Stalkers to be nerfed; I'm posting this because I want StJ to be buffed, but it should be done in such a way as to avoid making StJ Stalkers too much stronger.
*What with Arcanatime and the difference between power activation times and the point in the animation times where damage and debuffs are applied, I'm not 100% sure it's actually possible to land all three attacks before the debuff wears off. I'm being generous and assuming you can, but using Sweeping Cross instead of Spinning Strike because the former is faster.