I agree with chris and dthorne. Fusions are a way to get guaranteed legos. Open shards during the fusion tournaments, but don't expect a lego from the shard, expect 250 points in the champion chase.
That are all legendary champs I own. Vlad fusion, Visix daily, Arbiter quest, Yoshi fusion, Drexthar 3v3 arena basar, Rhazin fusion, Ninja free, Scyl daily, Teela shard (my first lego in the game, ranked as worst lego of all by Ash), Gamuran shard, Ruel fusion, Duchess shard, Ghostborn shard, Lyssandra shard, Zavia shard, Cleopterix daily, Aleks free, King Garog shard, Kantra shard, Yannica clan shop.
So exactly 50% of my legos are from shards. Fusions and other free stuff like daily rewards are a great way to get champs. Duchess was a lucky pull obviously, but I got here quite late, shortly before I got Cleopterix as day 450 reward, so my account progression was not bound to her.