Not only are you protecting your life points without losing your Stadium/Midfielder combination, but you are also giving yourself a bit of protection from direct attacks
From a game design perspective, I can understand why including a creature type into a Limited environment that wasnt going to support it was viewed as problematic in the short-term
You choose which one because you control the enchanted permanent
When youre fully resolving either, the deck feels like it has the teeth to go toe-to-toe with the top dogs, and when you arent, its a bit of a mess much like its sister strategy, Tistina
A one-sided mana doubler that existed before the likes of Caged Sun or Crypt Ghast, Nirkana Revenant fueled many a powerful X spell while also being able to put opponents down with the aid of a Whispersilk Cloak or Akromas Memorial
While it has limitations with its effect negation and shuffling into the deck, its ability to Special Summon another Gladiator Beast from the Deck can facilitate combos and maintain board presence