There are multiple very relevant threats which survive Lightning Bolt but die to Heat, such as [card]Yawgmoth, Thran Physician, Omnath, Locus of Creation, Crashing Footfalls, Primeval Titan, most Planeswalkers, Yorion, Sky Nomad, and the list goes on
(Look at the top three cards of your library, then put any number of them on the bottom and the rest on top in any order.) Whenever this creature attacks, you may return another creature you control to its owner's hand
Frequently Asked Questions How much is Running Is Useless worth
Athena confirmed that the set includes cards specifically designed to re-prepare your own creatures and unprepare opposing creatures
I also expect this to get better over time with legends entering the cube at a faster rate (per instance) than non-legends