The benefits of the Great Hall are applied across the six modes in the game, the way to obtain that benefit is tied to only one source, arena. To me that seems a somewhat unbalanced acquisation method. 

Before people jump in with over helpful suggestions such as "git gud on arena", this is not about the state of arena, it's looking at the way you obtain player power and exploring that imbalance. 

Suggestion would be in all modes allow the chance to obtain medals, such as campaign a low chance due to the very high levels of farming; through to CB chest giving a significantly more number as there is only 1 or 2 per day. Not flooding players with medals, but a flow that will allow over a decent period of time the gradual completion of the Great Hall.

Also what would need to be addressed is the medal colours, which could be resoleved that once all bronze completed you then get silver, and once all silver you get gold from the different sources. I would not suggested a free-for-all gold medal fest.

I've been playing for a few months and do enjoy the game but this is the one area that does seem to be a flawed way of providing player power.