First of all, John 1:1, Paul (Col 1:15), and the writer of Hebrews (Hebr. 1:3) all say that Jesus is God. Jesus claimed to be God, (John 10:30) telling the disciples that having seen Him, they had seen the Father (John 14:9). Even God called Jesus God in Psalm 45:6 which is repeated in Hebr. 1:8. The first chapter of Hebrews is devoted to this issue. These claims can not be refuted. If Jesus isn’t God in the flesh then the Bible can’t be trusted.
Even more importantly, people who insist that Jesus is anyone other than God Himself fail to understand the theological implications of what they’re saying. Think about it. Only God is sinless and only God can forgive sin. And yet the Bible makes both claims for Jesus. If someone else could have saved us then God could have sent anyone. But there wasn’t anyone else, so He had to become man and do it Himself. It’s the only way we could be saved. So if it wasn’t God Himself in human form who died on that cross then none of us is saved. It’s that simple.