I rode that left thumbstick hard during the 8ish hours to platinum Resogun, and I've used it a bit less intensely about 20 more hours across Killzone, Knack, Need for Speed, and Warframe and I see absolutely no sign of wear like that. My thumb even felt slightly blister-like sore from some of those Resogun sessions. I feel like if the cover was going to quickly give out it would definitely have already done it.
I do have that groove around the base of the stick starting to building up, but all my gamepads have that. It doesn't really effect the use of it at all and I look at it like a cool battle scar, a sign of the controller fulfilling its role during some intense gaming marathons.