My take is that Apple was not over using skeuomorphism to much excess at all (except for a few notable over uses like Contacts, etc.) but might have lost sight of keeping things consistent and up to date. Not that so called ‘flat’ design alone is a solution to anything! What does matter is good design and understanding humans and how they operate. Flat, skeuomorphism, a combo (probably the best solution over all which, Apple seems to have missed entirely!), or other approaches.