Late but [a+b] is easy to jg or sidestep on reaction and a+b is punishable especially up close. If you use it at tip range then some characters will have a harder time hitting you but it's still not good to spam at all.
bb is viable vs everyone in the cast. It's not good to spam it out but it kills backstep nicely which is extremely important.
I know AB hold sucks i was just trolling..... And bb will catch algol at the start of his step animation. So its more viable vs him. I think vs other characters its a huge risk. I use bb as a zoning tool, and not for backstep punishing. If i read a back step i usually 66b or c3b