For the following assume you're using the un-expanded watchlist without grouping enabled (therefore the default preferences a new user will see):
The current behavior of Flow is to create an entry in ones watchlist for each and every action. That means every comment (even if it's on the same topic) creates a new entry. Therefore the watchlist is quickly flooded by dozens of Flow comments making it very unclear and nearly impossible to quickly find other pages that have changed in the same period of time.
Flow should therefore (as is the default for normal Wiki pages) only list the newest edit to each watched board. The current behaviour can be kept but should only be enabled when choosing the expanded watchlist from user preferences.