When Yui was in Japan, she was a Shiatsu specialist, and maybe her clients were mainly Japanese women, so her massages might have felt light and soft. Given her petite frame, it's hard for her to provide deep pressure throughout the entire session. Now she's focusing on applying more pressure to specific pressure points, which should enhance the experience.
In Japan, Shiatsu relies more on the strength of the hands, which might not be Yui's strong suit given her petite frame. If she could incorporate the power of her elbows and knees into her massages, I believe she could greatly improve. Renee should definitely teach Yui the art of back walking on knees.