I think it was equally "hard" for both since both share the same human nature. The contexts of the Jew vs the different Gentiles where different, which means that they each expressed their acceptance/rejection of the new covenant in outwardly different ways. This doesn't change the underlying human nature shared by all. For both, "the way of the sinner is hard" and "all have sinned and fallen short..." According to the new testament, there was a spiritual blindness over the Jews eyes and they in effect preemptively mostly rejected Jesus as Christ.
The Jews did NOT accept the new covenant. Only a few did. They were expecting a earthly king to save them. When Jesus died ... They could not believe. He claimed to BE God and they called it blasphemy. Gentiles accepted the new covenant and grace. The Jewish are waiting for the 1st coming of the Messiah.
The Jews were a stiff necked people they constantly continued to turn their backs on God. They either didn't understand or read the Word of God. The only ones who did were people like King David,Moses,Joshua,Abraham,Issac,Jacob,Elijah,Elisha, etc.etc. and all of God's prophets. Therefore God sent His Son Jesus to die for the sins of the World. But just like the Jews a lot of the Gentiles were the same way especially today. The Jews are God's Bride to where the Christians are the Bride of Christ.