The problem with the KJV is that it was translated from Jerome's Latin Vulgate, which had errors in it. The more modern translations are done as the result of the range of manuscripts that are available, and so the best translations possible are made. Also, in many cases, the Greek words carry several meanings that can alter the sense of a passage depending on which meaning is chosen. This is why modern translators also consult the writings of the Church fathers to see how they interpret the passages. Then the translators have to make decisions on what they believe are the best meanings.
Of course, the Early Church Apostles in the First Century did not have the New Testament written down. At best, they had a collection of Paul's letters and the Torah. But they had the added advantage of being present when Jesus was on earth and had received His teaching verbatum. Paul was not part of that group, but he received his teaching by direct revelation from the Holy Spirit in a way that no-one else had or ever will have. That is why his writing is considered Scripture now.
I think that it is good to consult as many of the available versions as possible when trying to interpret difficult or hard-to-understand passages. Having a Greek New Testament also helps. I have an interlinear Greek NT, KJV, Revised, NASB, Jerusalem Bible, NIV, and Amplified, plus some commentaries. Among those, I can get a pretty good understanding of what is meant.