I've only ever won the deathmatch once, and that was when I wasn't even trying to win! Got a trident, although that is a very good magic item... even when it ends up on a priest!
Maybe you got something different because someone you killed during the tournament was carrying something else.
I do think the AI wastes too much on the arena. There isn't a whole lot to gain from it, if the prize is always that trident. Since it's "too the death", all but one of the opponents will die even if you don't bother to show up. The AI tending to send pretenders, prophets, strong units with items, etc., mainly just ensures that all but one of the AI's will lose a useful unit. Seems like they should usually just send a regular fighter type who isn't leading anyone at the moment, and only occasionally risk someone really tough (and good to keep alive).
PvK