Yossi, the problem with your theory is that there was rampant avodah zarah throughout Israel from the times of Joshua up until the first churban. Most Israelite homes in Judea and the north that have been uncovered in archeological digs had little statues of astarte and all of Shoftim involved Bnei Yisroel being punished for idol worship. Ironically, two things disappeared with Ezra’s return, idol worship and nevuah. Neither is mentioned in the Second Temple period.
By the way, two other things changed with Ezra’s return, and noone really knows why. 1. We adopted Babylonian names for months that previously had no name I.e. Tammuz 2. We adopted an Amaraic form of block letters ( our current printed alphabet ). All writing prior to the churban was in what is called paleo-Hebrew, which looks starkly different.