If you think Mobility and Flexibility are the same, could be one of the reason you are stuck in the same range of motion with no results and possibility of an injury.
Doing only stretching for flexibility pre/post workout will temporarily improve the length of a muscle, as the muscle will return to its original state and results will be temporary.
Utilizing Mobility exercises and in particularly prior to exercising will be more effective because it is based on movement and control. Incorporating mobility exercises in your daily regime will increase and strengthen your range of emotion while preparing your nervous system. This new strength and mobility will be carried over to your workout and next sessions, to continue to improve performance and joint health.