Honestly, it's sad that the reward for getting 252 stars on the nightmare campaign is one lousy sacred shard. This is a MAJOR achievement in the game, and getting one sacred shard for the effort is not even close to worth it. 

My suggestion: give the players a select-one-champion choice upon completion of the entire campaign. Just as we got to select our new game starter champion, let us select our end game starter champion. I guess you could restrict it to a non-void or non-legendary if you want, but make it a real, actual reward. The same way that Arbiter is an actual reward for completing all of the missions, we should get something just as good for perfecting the entire campaign. 

You know one sacred shard is almost worthless, so please make this change!