Yes, it became outdated after several years in use (6 on the iPhone?) and perhaps even didn't age well looking back on it. But for the time it was used it was definitely not a failure. Design preferences change, it doesn't mean everything that is replaced is automatically deemed a failure.

And unlike many other design trends that are purely about aesthetics, skeuomorphism also had a practical aspect: people had to "learn" a whole new way of interaction with these devices and using familiar shapes and textures helped. The "Start" button in Windows is called like that because people literally needed to be told where to start with the "futuristic" GUI.