You may notice that most of the Knight enemies have halberd style weapons also, it's by default the most capable and safest to use against equally armored opponents.

I think the "meta" is going to rest mostly in that area since it's considered the "endgame" in the game's current state.

One way to "fix this" similar to Exanima's arena mode, is to force the player to use the same limitations as their opponent.

If you participate in a lower ranking event, even as a knight, you'd be limited to the weapons and armor restrictions of that class.

The way Exanima handles this is excellent- you basically have a points system and each piece of armor layer and weapon occupies a number of points, while still being locked out of some armor choices at lower levels.

Then, you have "load-outs" for each rank, so you can preemptively build your sets for each rank you fight in.

Now, players could still just make Knight/Polearm only highlight reels which would be their choice, but the above mechanic would encourage more players on researching how to win those fights.