The lifespan of a SCUF thumbstick will depend on how often you use your controller and whether you are hard or light on your thumbstick pressure. Similar to a marathon runner with running shoes, if you game 8 hours a day and are heavy on your thumbsticks, then maybe only a few months. HOWEVER, SCUF created the interchangeable thumbstick area; which allows you to replace your thumbsticks in seconds. Because the thumbsticks are removable, SCUF focuses on offering the optimal grip and comfort, knowing these thumbsticks can be easily replaced as they wear through use (similar to tires on racing cars).
SCUF thumbsticks are designed to offer the optimum grip performance and comfort without compromising too heavily on durability.
Standard Xbox One or Playstation thumbsticks are harder which provides some additional durability but less grip and comfort. This is because Xbox One or Playstation thumbsticks are not removable with the standard controller and therefore are not designed to be replaced (consider the racing car analogy).
General rule of thumb: as grip is increased through softness, comfort is improved, and durability is decreased.