I think it’s fair, I wish there were more events like this honestly. Considering the hefty amount of shards required for new legendary event skins and mounts.
It rewards people dedicated to playing the game not just being lucky. I have over 7 rounds on the board by focusing on quests and I had most of my heroes one game from leveling before it started. Yet I haven’t won a single new legendary item for the event (some duplicates but nothing new) but I have earned enough shards to get 2 or 3.
Plus feeling like you are getting some rewards might make you more inclined to keep playing. Would people keep playing the lottery if it was just the grand prize and everyone else got nothing?. Probably not.