Champion's Trident grants Quickness, and you get lots of experience for winning the match. In early game, the victory guarantees a heroic ability, and sometimes Quickness is worth losing both hand slots.
Most of the time, especially in competitive multiplayer, this isn't enough. There are many reasons for this.
1) The Trident isn't good.
Quickness gives twice as many actions per round, which also means twice the fatigue every round without doubling the reinvigorating effects of other equipment. Generally anything with encumberance over 0 will start suffering very quickly, which lowers both attack and defense directly and allows for armor-piercing hits and increases the chance of them occuring.
2) You need hand slots for other stuff
In addition, the champion can't use a shield (and thus can't get Fire Shield or Awe from Charcoal Shield and that Shield of Glittering Gold or whatever it was) or a weapon that affects an area (Fire Brand, Frost Brand, Shadow Brand and few others). Fire Shield and Awe are both excellent abilities against chaff, and AoE weapon might be enough to make quickness worth it if you can afford the other equipment you need.
3) Mages get nothing
4) The Arena is dangerous
Not only do you have to survive against everything else sent to the arena, but your opponents might decide to send guys equipped with items that disease (bane venom charm, rod of the leper king), curse (eye shield, knife of the damned) or cause afflictions to the user (eye of aiming) - and are picked up by the winner. I'm sure some guy in multiplayer has been really screwed over by "winning" the arena.
I made a mod (Mark of the Champion, see sig) that changes the prize like so:
- it only requires head slot
- the trident is a bonus weapon, like dancing trident or stone bird
- it grants a special helmet that also increases body protection by 5
(- it still grants quickness)
Even with these changes, several people thought it didn't do enough to improve the arena. There's a poll in the mod's thread, but it didn't get much attention.
P.S. Sorry for advertising my mod.