While you are right, if a supplier is actively working against a customer, it is going to create problems. There are always a million things outside of the contract that matter. If the customer exceeds capacity planning volume, that gets resolved outside of the contract. Most suppliers will bend over backwards to help the customer. Will Samsung? Maybe.

If I were Apple, I'd prefer a supplier that has a natural incentive to be a great supplier rather than one that only has a contractual obligation. In the long term, contracts are as hollow as wedding vows. The relationship between a customer and supplier must be mutually beneficial with aligned interests.