If Featured 5 Star Crystals Exist...
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...Why not make featured four and 3 star crystals? Like for example for 3000 4-star shards you have a chance at the featured champ, along with subfeatured, as a four star. For 3000 3 star shards, the same, but as a 3 star. There probably is a reason why this hasn't been done but I'm still curious.
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There's also that "4* champions are becoming obsolete" argument which I personally don't believe but is still nonetheless a possible factor as to why there isn't a 4* featured crystal.