Question about Psalm 2 (You are my Son, today I have begotten you)

Christians have understood Psalm 2:7 as a reference to Jesus as the begotten Son of God. But how could this be if Psalm 2 is God speaking to the King of Israel? The response is typically that this verse refers to the Messiah *as well* as the King. But there are two questions that come to mind in regard to this answer: 1. How can this text be used to show that is Jesus unique in his sonship if it also applies to the King? 2. Hebrews 1:5 applies Psalm 2 to Jesus in order to establish Jesus' superiority over the angels. But wouldn't this also prove the King's superiority over the angels as well?