I have the same car and my experience matches yours. Lane assist is just a tiny nudge, and I've never had the emergency braking kick in. I wonder what causes the different behavior?
To be fair I was going 70mph at the time. It could be a small nudge but at 70mph feels worse. I also had only owned the crosstrek for about 5 minutes at that point and I couldn’t figure out how to turn it off as well, didn’t realize buttons were placed on the ceiling.