Paul spoke in response to a direct address. This is not the same as a prayer to Jesus. Your point is a 'false analogy,' a common logic fault.
In Stephen's case the Bible says: "54 When the members of the Sanhedrin heard this, they were furious and gnashed their teeth at him. 55 But Stephen, full of the Holy Spirit, looked up to heaven and saw the glory of God, and Jesus standing at the right hand of God. 56 “Look,” he said, “I see heaven open and the Son of Man standing at the right hand of God.”"
He saw Jesus and God in vision. [Note that the verses describe Jesus as at God's right hand and not as God himself.] Stephen addresses his petition to a Jesus he sees. This is a conversational transaction. If you pray to Jesus, then shouldn't you follow the pattern set by these verses, and only address him when you SEE him?
Your point is poorly thought out.