Then what you are really saying is that God gave guidelines for the early church, but He didn't understand then how things were going to be different today in modern times. But, God does not change. He is the same in the past, today, and will be the same in the future concerning any specific topic. I believe that if He said in His word that churches ought to run a certain way during that time, then they ought to follow the same guidelines today. No, His Word has not changed.
Men are the ones who change.
Because they do not follow the Word of God. That is why most churches are carnal today. You say it is because of sin. That's is true, but sinful living is the result of not following God's Word. I am excluding all those that preach a false Christ and false doctrines of salvation.