Rek'Sai seems a bit lacking
Even when I am 4/0/3 I still feel heavily behind on damage and cc. I feel like if her burrowed Q had a slow or if anything had more cc then she would be viable again. As a bruiser, she needs to actually stick on to her opponents to do something. She can't just burst. I don't know exactly what she needs but she needs more than her basic knock up.