Were Peter and the eleven less spiritual than Paul for not seeing the change God was making?
No. Peter and the eleven were not less spiritual than Paul for not seeing the change God was making. God had not yet revealed to those Jewish believers at Jerusalem that He was doing something different. Once He reveals His secret purpose, believers are to believe it.
Les explains that the Twelve in Jerusalem eventually admitted Paul was right and that the Lord was evidently doing something different. But he insists he is not taking anything away from the Twelve's spiritual relationship with God. They were not out of step or less spiritual; God simply had not yet revealed to those Jewish believers that He was now turning from the Jews to the Gentile world. Using Deuteronomy 29, Les says the secret things belong to the Lord, and He reveals them when He is ready; once revealed, we are to believe. Peter and the eleven were in that position.