“In the early Christian Church, everybody was considered “Catholic”
Yes, and the “Catholics” of the early Christian Church believed in the true prescence of Christ in the Eucharist just as the Catholic Church of today continues with this timeless teaching of Jesus:
St. Paul himself could not have been more clear: 1Cor 10:16, “The cup of the blessing that we bless, IS IT NOT THE SHARING OF THE BLOOD OF CHRIST? And the bread that we break, IS IT NOT THE PARTAKING OF THE BODY OF THE LORD?”
I agree, the non-Catholic Christian Churches of today hold little in common with the original “Catholic” church of the apostles.
The Catholic Faith is defined by the Athanasian Creed. While the faith as defined in that creed is presumably held by most members of the Roman Catholic Church, it is likewise held by members of other orthodox Christian denominations.