First: over a year of grinding and I have never seen trident on a bronze arena spin (not 'won one', just 'seen one'). Maybe just bad luck.
Second: can there not be a middleground between grinding to get what you want and having fun? Playing 100 games against a Half-Blood with the same deck, which has the same strategy regardless of who you play, seems boring-er than boring.
Third: If I understand the concept of rare-farming in other games, it is impossible in Elements because you cannot pick your matchup ... so what's the deal, yo?