Matthew 28:18

Jesus came and said to them, “All authority in heaven and on earth has been given to me.” -- Matthew 28:18 (ESV)

Out of context, it seems like Jesus says that God handed over all his authority to him so that he could become the new God.

The fact that Jesus authority was given by a greater God and did not come from himself, proofs that Jesus was not the Almighty God.

According to NAS Exhaustive Concordance, the Greek word didómi which has been translated to "given" in the ESV could also mean: granted, allow or permitted

Nothing in the context suggest any kind of handover or giving up such that the old God, no longer have any authority because it was "given" to the new God. Neither is Jesus competing with another God.

John 16:15

All that the Father has is mine; therefore I said that He will take what is mine and declare it to you. -- John 16:15 (ESV)

Out of context, it seems like Jesus says that God handed over the whole creation to Jesus and perhaps the Father is now retiring, but that is not what Jesus said. If you read the full chapter you will notice that Jesus is talking about the Holy Spirit (John 16:13) and that it is "the Spirit" that "will take what is mine and declare it to you".

Jesus rightfully inherited God's creation as "the Son of God", not "the Son as God".

Neither did God the Father retire, nor did Jesus took over the Father's role. Instead, Jesus is God the Father's servant or steward (Isaiah 42:1; Acts 3:13 (ESV); John 4:34, 5:19, 6:38, 10:37, 14:24, 14:31) who has been given all authority so that he may glorify God the Father (Philippians 2:10). This implies God the Father is still in control and Jesus still need to submit to his God.

So Jesus said to them, “Truly, truly, I say to you, the Son can do nothing of his own accord, but only what he sees the Father doing. For whatever the Father does, that the Son does likewise. For the Father loves the Son and shows him all that He Himself is doing. And greater works than these will He show him, so that you may marvel.” -- John 5:19-20 (ESV)

Nebuchadnezzar received the following revelation:

And at the end of the time I, Nebuchadnezzar, lifted my eyes to heaven, and my understanding returned to me; and I blessed the Most High and praised and honored Him who lives forever:

For His dominion is an everlasting dominion, and His kingdom is from generation to generation. All the inhabitants of the earth are reputed as nothing; He does according to His will in the army of heaven and among the inhabitants of the earth. No one can restrain His hand or say to Him, “What have You done?”

At the same time my reason returned to me, and for the glory of my kingdom, my honor and splendor returned to me. My counselors and nobles resorted to me, I was restored to my kingdom, and excellent majesty was added to me. Now I, Nebuchadnezzar, praise and extol and honor the King of heaven, all of whose works are truth, and His ways justice. And those who walk in pride He is able to put down.

-- Daniel 4:34-37

Daniel would not have written down Nebuchadnezzar's revelation if he did not agree. The Most High God reigns forever. There is no hand over.