Yes, that is what we are trying to ascertain here - What Church?
Now, if Christ did establish a Church, that means that that very same Church exists till today because He promised that the gates of hell will not prevail.
Indeed the church that sent Paul and Barnabas to speak to the council of Jerusalem was a Church.
But, the fact that they needed to get an okay from the council in Jerusalem meant that this church must be part of the a bigger Church of which the church in Jerusalem is also only a part. Otherwise, the ruling of the council will not be binding on the Church in Antioch, the church that sent Paul and Barnabas.
So we see several churches in infancy : Smyrna, Antioch, Jerusalem, Rome, Ephesus, Galatia, etc. But, they all belong to that one Church that Christ established because these Churches were all founded by the Apostles and Paul. The foundation of these churches was in response to Christ commisioning: Make disciples of all nations baptizing them in the name of the Father and of the Son and of the Holy Spirit.
Very early on, we see the Catholicity/Universality of Christ’s Church.
What we also see is that there is a central body that determines doctrines. Paul could not make a decision on his own, and neither could Barnabas. The Judaizers which belong to the church in Jerusalem could not impose their own decision too.