The problem was Copernicus was at best not as strong willed as Galileo, or at worse, a frightened hypocrite. During his life he repeatedly championed the geocentric theory, but wrote a detailed exegesis on how in reality, the solar system was heliocentric. He feared, and perhaps (?) rightly so, the wrath of the Vatican. I believe on his death bed he allowed his heliocentric theory to be published. Galileo on the other hand, and with the support of the scientific community, stood his heliocentric ground, and suffered the consequences. Fortunately for him Urban VIII was a believer in the heliocentric model and denied the chorus of Cardinals howling for Galileo's head.
Yes, not only did the Greeks understand that the earth is a sphere, but Eratosthenes proved it by putting a stick in the ground.