Mythic rares are designed to feel special, whether that means a story-important character, a game-changing threat, or a card so powerful that it may just end the game outright if left unanswered
Unsurprisingly, there's only 4 cards that reward you specifically for having 7+ power (e.g
$100 List We've made a few major upgrades when bumping the price tag to $100: Puresteel Paladin is arguably the single most important upgrade to the deck, drawing us cards but most importantly removing equip costs which saves us tons of mana
Nightveil Specter 4
Take a look at MaRos articles describing new sets - he does not just dump the image gallery and say let me know what you think - he describes the sets design goals, the mechanics, why they were chosen, how those mechanics were placed in each colour, the limited archetypes the set was designed around, some anecdotes about the design process, etc
Successfully mutating a creature in play does not make it a new creature entering the battlefield, even if you just turned a 1/1 token into a 6/6 flying trampler