According to
Philippians 2, he conceded his Divinity in order to effect reconciliation, when we had left God. Why can the church not do likewise?
He absolutely did not concede his divinity. At no time did Christ ever stop being God the Son. In Philippians 2, you're probably talking about these verses:
5 Have this mind in you, which was also in Christ Jesus: 6 who, existing in the form of God, counted not the being on an equality with God a thing to be grasped, 7 but emptied himself, taking the form of a servant, being made in the likeness of men; 8 and being found in fashion as a man, he humbled himself, becoming obedient [even] unto death, yea, the death of the cross.
He came to earth both fully human and fully divine. He humbled himself in his human nature and became the sacrificial Lamb of God to atone for the sins of mankind. He did this as it was foretold because mankind could not offer a sacrifice that would be sufficient to restore the union between man and God that was broken by the disobedience of Adam and Eve. Mankind had nothing to give by which to merit the sanctifying grace that had been lost, and so Jesus paid the price on our behalf.
This was not a concession. It was a supreme act of love on his part and obedience to the will of his Father. Conceding is to give in to something for the sake of ending an argument, or to admit to something, or to acknowledge defeat or acknowledge having been wrong, etc. Jesus did none of that.
Are you not aware that the Creed and the doctrine which forms the basis for it was a process of compromise, collaboration and consensus among all parties involved??
You mean compromise, collaboration and consensus among the bishops at the Council of Nicaea, right? It would have been heavy on collaboration and consensus with little or no need for compromise. That's because they were all solid Christians working with articles of faith that were clearly laid out in apostolic teaching. There was no dispute among them, except maybe as to the best way to state what they wanted stated. The Nicene Creed is just an in-depth and expanded version of the Apostles' Creed. (The Apostles' Creed itself is an expanded version of the even more ancient Old Roman Creed, which was based on the Profession of Faith that was recited by those being baptized very early in Christianity.)
In any case, the Nicene Creed was written with the primary objective of eliminating any possible misunderstanding or misinterpretation of God as Father, Son, and Holy Spirit. It was produced in order to more fully and specifically articulate the profession of Christian Faith.
The Catholic Church has nothing to concede on matters of faith and morals because it never departed from apostolic teaching and has never been without the guidance of the Holy Spirit in that regard. This is the infallibility of the Church. Our Protestant brothers and sisters should look into conceding that they have been mistaught, and come home to the fullness of faith where "
...there will be one flock and one shepherd." (John 10:16)