Apparently MASTER was playing in this video, and it seems like the way fatal rush is broken down is fatal rush stun, then a string of normal strikes which can be counter (which would explain in other videos people holding during the fatal rush stun despite being told fatal rush is unholdable) followed by two more hits that cause fatal rush stuns. So right now the game seems to give you a small window to break out of the fatal rush if the string is continued, which gives you a choice to risk getting mid counter held in the small window for the big combo into break blow or utilize the unholdable first fatal rush stun and go for a launcher.
Also, it was really nice to see competent gameplay and not just two people mashing lol.
Edit:
Ok uh, Kasumi didn't do standard hits after her first fatal strike like Jann Lee and Helena did. Soooooo I guess it depends on the character? Or maybe it was unintentional for the other two because Kasumi's is just a bunch of teleport attacks.