I’ve always wondered about this. I have always thought that there should be a Chiluk between a latecomer saying Borchu (in essense, being Pores Al Shma according to some Shittos) and randomly saying Borchu at the end of Davening whether or not there were any latecomers, which is the Minhag in EY.
old man: I was told it’s not borrowed from the Sephardim. It’s the Shittah of the Gra. Many Minhagim in E”Y are against what was standardly practiced in Ashkenaz because the Talmidim of the Gra were the first to come there.