I use mean streak but I'm starting to feel clean cut is the way to go in this MU. I use mean streak almost exclusively so my thoughts will come from that MU for the most part.
Cassie is in complete control in the neutral at all times, forcing you to come to her. When Kabal is the one trying to work his way in it can actually cause problems due to his lack of decent advancing moves. You have to play pretty patient in this MU and have to just play a solid grounded footsie game until you can get your pressure started, then really make the most of every touch.
J2 is only good for reading low shot at footsie range as Cassie actually has a relatively easy time dealing with it between her s1 anti air and trip guarding with B1. Her footsies are also really good, meaning she's one of the easiest characters to whiff punish your own B1 with.
Her shimmy game is also worth taking note of, B1 staggers into walk back B1 will actually make a lot of your buttons whiff, besides a very well timed F2 or having to throw out B1 at a range where you wouldn't really use it. Be careful of poking out of her pressure, she can whiff punish your pokes in the exact same way you can with hers.
IA Straight Buzzsaw is good for a check every now and again, but Cassie can just change the timing of the gunshots so she goes under it. This isn't one of the MUs where you're going o be throwing Buzzsaws all day, even on a life lead.
Clean Cut could change a lot of this though, I feel like this is one of the only MUs where the utility of air Buzzsaw might actually make it the go to variation, but I haven't really played it out enough to say for sure.
I like using hook sword restand in blockstring in this mu. Safety is key or this chick will blow your back out for mistakes. IA straight is good but I prefer whiffing an air normal into down saw from time to time to catch her. I totally agree, chucking metal at her isn't what's going to win the match....I'm still fleshing it out but i agree Cassie dictates the match from start to finish, at least that's the way it currently feels