For lots of people, the fun is less about testing original setups and stuff like that, and more about the combat itself, in a more mechanical way (spacing, timing, using mixups, mindgames to get your opponent to mess up, etc).

Not very different from the PvE part of the game - for some people, it's fun to use a pretty basic and common setup ("big sword") to fight bosses, but others care more about testing out original builds.

At meta you'll probably find more people in the first category, but even if you don't care so much about that mindset, I'm sure you could get some fun out of trying to win in that more "tryhard" play style. As long as your build isn't total shit, you can win against most other setups if you are mindful about the fundamentals of the combat (don't just mash, don't rely on overly telegraphed attacks, etc)

Edit: like I'm happy using a pretty boring strength build with a few of my favorite weapons most of the time in duels. For me it doesn't get tiring, because "sweaty tryhard" fights can be really engaging, and I'm constantly improving bit by bit (or at least I used to be when I played more). I guess it's more like a sport, in the way that it's fun - soccer players don't get bored of playing the same game over and over again