It's a bit strange to quantify "iconic" -- is it in the boxoffice (which must count popularity of the movie or at least interest at the time) or do you count what a particular film's impact was on movies and culture?
1988 is a good example: The big event movie that year was Roger Rabbit. A huge accomplishment with big names attached (Spielberg/Zemeckis) and the entire world of cartoons. Most people can't even watch that movie now. However, a much less successful film that year was Die Hard, which had a huge impact on all action films that followed for many years and is arguably one of the best action movies ever made. Now I think most people would say Die Hard is the iconic movie of 1988 -- but in 1988, most people would say Roger Rabbit was the big one.
1999 is somewhat similar: TPM was the big get that year -- but The Matrix was such a superior movie is every way and far more impactful on movies. It even made Empire's list.