There were lots of changes between GGXX iterations too 
The biggest change in GGXX was from #Reload to Accent Core, IIRC. What they've done in BBCS is more. Some characters have really changed up and have different sets of combos now. Also the obvious MUCH-NEEDED balancing.
But the difference between GGX and GGXX is that the roster was pretty much doubled. I expect a Blazblue 2 with 20+ cast in the next year or so.

From GGX to GGXX, I-No, Slayer, Bridget, and Zappa were added. Four characters. From BBCT to BBCS, they added Tsubaki, Hazama, Mu, Makoto, and there are at least two more characters coming (I forget their names). That's six characters. Only one of those characters, Mu, is a character using another's sprite. GGXX later added Order Sol, Robo Ky, and A.B.A. Only one of those is using an original sprite.
Frankly I would rather see Battle Fantasia 2 than another BB update anytime soon.
