Apparently you do not believe the Creed which is said at every Mass:
“…God from God, Light from Light,
true God from true God,…
For us men and for our salvation
He came down from heaven,”
All Catholic priests, bishops, cardinals, Pope, declare this when celebrating Mass.
Heaven proper is the Beatific Vision of God, God is the the source of the Vision, Paradise is a place where the Saints inhabit. God does not have to come down, because He is pure Spirit. Paradise, the place or state of happiness with God involves the humanity of Christ which is united to to His divinity. Jesus entered time, assumed human nature, so we can apply human actions to Jesus because of His human nature, He was flesh and blood. In that sense God came down, because Jesus is human, occupies space, has blood and flesh, but He is God in His divine nature, the two natures can not be separated.
In His divinity, He is Pure Spirit, Omnipresent, Omniscient, Omnipotent In His divine nature, not in His human nature. He never was separated from the Father who is in Heaven. You never make this distinction So it is true that Jesus, a human with a divine personality entered our physical world, but as Pure Spirit in His divinity He never left His Father, or the Holy Spirit So the Church is right in her prayer because Jesus is divine, with human nature. He is always united in spirit with the Father. What you are saying is that Jesus, God, separated from the Father and came down to earth. Jesus never ceased to be God, Pure Spirit, sustaining creation, while He was walking the earth. I explained the best I could, and I can not make you understand. I am not contradicting the Nicene Creed which you quoted. In your mind, I am. The Church has to say, that The Son of God came down from Heaven to assume human nature God is Pure Spirit does not occupy space or time, He creates them.
He entered time that He created, how else would you say it in human terms? Jesus, God, one with the Father and the Holy Spirit never separated with His Father or the Holy Spirit, we have our existence in God. Human terms don’t always capture the complete truth, or describe the complete truth, but what they describe can be the truth in so far as they go. The Trinity is a Divine Mystery of the Church.