1st, I disagree that Bronze league is weaker than AI3. I think it could have a better reward, lets say, minimum 10. Anyway, not really important.
About that GREAT challenge... no one will fight AI0 with upped deck (no fun), but no one will fight AI6 with starter deck. Lose, lose, lose again is also not fun if you cant win some. I hope we can have a balanced Platinum league, but dunno:

This was Gold League. Platinum could be worse. 1st, I think its necessary to forbid Shards. A lot of games in higher leagues are boring and you just win by deck out. Also, I think its necessary to forbid Quantum Tower. Anyone can create a default deck with QT, packing lots of Steals, Explosions, Black Holes, etc, etc, and just insert the Oracle cards. If we dont have some limits, I think its hard having decks really built considering Oracle card.
Also, I liked the increasing HP loss. Maybe some balance will do it better (because this way lower leagues are more affected), but the idea is good.