soraka can't heal herself with W so the counterplay is to kill her

Then kill her!

Just shift your attention for 2 seconds. The ult doesn't last long.

if u burst sum1 b4 she can react u kill them

Yeah, the counter to Soraka is killing her. Eventually bursting her ADC faster than she can heal. About Kayle ult, it doesn't give a target CC immunity, so Morgana's bind or just any kind of hard CC can still give you a kill,, also, you can always try to bait it out, and then either change focus onto non ulted person, or back off and attack again when it's effect wears off.

Soraka has a lot more counterplay than just killing her, not that a lot of people realize that.

Soraka's heal is much larger and more efficient than kayles to be honest