Could deck-making in the Arena be changed like this:
- The deck is published only after you have played against it in the 'Test your deck' -section.
- The deck would remain in the same state as if it has rank > 500 until you have played against it and click a Submit-button.
This would allow the deck to be tested before it is submitted, which prevents someone beating your deck before you have ironed out the weaknesses.
A second idea, related to this but maybe too much:
Allow submitting the Arena-deck only after you have beaten it in a test game.
Would ensure that each deck is beatable.
(But this might punish less experienced players more, so maybe only for the Gold & Platinum decks?)