Your point is mute because paganism was here far before Christianity. This is true history , its not which came first the chicken or the egg. Jesus spoke against "Vain traditions of men" , he meant paganism on the head. Jesus was addressing HIS followers when he said in vain do you worship me ; I mean come on , these people were worshippers of Christ and God, but they were doing something wrong, they were into mixing paganism with the worship of God. You may think this means nothing , but to Christ it was blasphemy.
Doubtful. Stone came before people but blasphemy doesn't follow because a pagan used a stone before a Christian did. Christians did not worship Pagan gods, and Pagans didn't worship One God. That is the difference between Pagan worship and Christian worship. The two lived close together for centuries, and actually there are some pagans who are still active today.
Christ looked forward to the day when people would worship the Father in spirit and in truth. I would argue that this mattered more to him than what kind of building or accessories people use. Christs comments on the vain traditions of men were spoken to those who criticized Christ's disciples for not washing their hands.
How do you think Christ would respond today if someone said to him, "Look! Your disciples are worshiping in a building that has a steeple that was originally designed by a pagan!" Do you think Jesus would march in and start over turning tables, or do you think he would say, "You are thinking as men do. Hear me and understand! Nothing on the outside can defile a person, but the things that come out from within are what defile..."
If what comes from the inside is worship of the Father in spirit and in truth, then today's Christians are doing just fine whether their worship is in a school cafeteria with a flat roof, or under a dome--or a steeple.