But see my previous post. Peter and those who were with him were SHOCKED that they were “saved” and received the Holy Spirit after only “believing”. It was obvious that Peter and those with him expected there was more to be done before that would happen. It would appear that the experience Peter had with those at the house of Cornelius is what illustrated the difference and what prompted him to speak at the council in Jerusalem.
I don’t see Jewish Christians that became “astonished” can be stretched there is a new dispensation. Jesus already told the apostles His gospel was for all nations. The astonishment is more that the Gentiles now had the gospel too rather than the Gentiles were given a “better” dispensation.
We cannot ignore that in more than one place words like “also” and “no distinction” ride over any other assumptions.