What do you mean by action? I have seen more action in some relays than in most sports. Swimming is just like any other sport, with the advantage that it's easy to follow (I mean, even if there are technical rules, it's all about who touches the wall first) and is a skill that everyone has tried in their life so it's easy to connect. Just like athletics, gymnastics, cycling, etc.
To stay on topic, highlight of the day is McIntosh PB, but also Titmus slower than expected and O'Callaghan faster than Worlds. The 400 FR could be interesting.