I’m not sure if “many” of the new Christians were Pharisees. Christ had some very dire warnings for the Pharisees and I can only recall two Pharisees in scriptures who became Christians, Nicodeamus and Paul.
I will give this one exception, the Pharisees were legalists and some of these legalists may have been the very people who were advocating the Gentiles needed to be circumcised and follow the law of Moses. This was heresy to the early Christians who understood that you can’t pour new wine into old wineskins. The old system needed to be done away with.
If Christ gave his warnings to Pharisees it would follow that many of them would repent ...
Exactly and that was the big significance of 70 AD and the destruction of the temple. With that destruction, there were no more sacrifices in the Temple. With that, the ONE sacrifice of Jesus was shown to have completed it, and just as He prophesized in the Olivet discourse, the temple was destroyed, rendered stone from stone.