I think the arena is a really neat part of the game. But, of course, I always have suggestions
The Champion's Trident is sweet. Really nice. But not nice enough, for me, to compensate for the loss of a second hand slot on a combat unit (I would only want the Champion's Trident on a mage). The fact that it is cursed makes it interesting... but, combined with the fact that it takes up 2 slots... not great. If it was 1-handed, or had a couple extra bonuses (reinvigoration, armor-piercing), then I might consider sending valuable units to fight in the arena, but as it stands I don't want to get a valuable unit (except a combat mage) stuck with it.
Then there's the matter of the physical location of the arena. Shouldn't owning it net you some advantage? I mean, since it DOES exist in the real world, the magic and heat scales should certainly affect it... even if it exempted from Dominion strength. Of course, for all I know, maybe these already affect arena combat.
Next up: Arena Squad Deathmatch, in which you send a leaderless group of normal units of total combined size <= 20. And no routing is allowed!
-Cherry