Marx; good question. I’ve never met a rosh yeshiva who has said that American frei are not to be treated as tinokos shenishbu.
Israelis are where it gets thorny. Some go with rav shloml zalman and say that they have ample exposure in our time. Others go with the chazon ish, that we’re on a very low level of torah and can’t properly teach it to the point where one is no longer a tinok shenishba simply by hearing about the torah and seeing us keep it. The majority go with the chazon ish, in my experiences, with some (mostly brisker) either going with rav shlomo zalman or saying it’s a safek.