If tai chi feels to be easy, then you have not been training the authentic art.
No form of exercise is easy.
If it isn't a challenge, then it isn't exercise. And it sure isn't tai chi.
Tai chi works your body at a greater intensity than your usual level of daily activity.You become fitter and stronger.
As you adapt to meet the demands of the training, the tai chi becomes more difficult; encouraging constant growth and development.