While I agree that there are indeed game changing champions, I feel that the beauty to the game is working with what you have to slowly build up your account.
The one thing that helped me a lot was hitting UNM and NM daily. With the amount of shards you can get from CB, your chances of pulling the very good ones increase a lot.
Honestly I have about 13 Legend and even though I have the champs to make a ultimate Clan boss team , doing more than 5 mil damage with one key is a struggle for myself
My point being, there are you tube videos of beating much of the game with Rare champions with the right gear. With the opportunities to collect all the many Legendary and epic heroes in this game for free just stick to it and grind it out. Your going to get alot of sacred free shards along the way and save them for a X2 event
Your Epics and Legendary champs will come by more than just shard means
But I personally I find with summoning that it seems like there are times when some champions are more pronounced to get from shards than others
If you see that just take a break and try again another time