What Church did the thief on the Cross that established a sincere relationship with Christ go to?
He went with Christ.
He had the real thing right there.
Christ left his apostles behind to make a church for anyone else not so lucky.
You're missing the point. The Church is the Divinely established manifestation of Christ's everlasting presence in the world after His death and resurrection.
This is the point of one of the most powerful allegories in the Gospels: the feeding of the masses with the loaves and the fishes. The loaves of bread and the fish in this Gospel passage represent the Old Law and the Prophets. Under normal circumstances (human limitations) these could never "feed" thousands of people, but through grace Christ can do this easily. And yet the Divine plan did not involve the redemption of man all at once. The numerical items in that Gospel have an important meaning. After eating all they needed at that point in time, the crowd of several thousand people left enough behind to fill twelve baskets. This represents the deposit of faith that would be revealed over time through the Church of Christ, represented by the twelve apostles.
Catholic doctrine on this is very clear, in terms of the importance of an institutional Church. If you eat your loaves and fishes (i.e., you accept what Christ offers right then and there) and settle for that, you've missed out on that part of His grace that comes from the twelve baskets.