Multiple finality counters on a single permanent are redundant
At the beginning of combat on your turn, you may have Gogo, Mysterious MimeGogo, Mysterious Mime become a copy of another creature you control until the end of the turn - but since Gogo keeps its name, you're free to copy legendary creatures too
The odds seemed better, or at least more evenly distributed, with Prismatic Evolutions
The creations of the hand are confined by reality
You defeat your opponent if you reduce their life points to zero, or if they've run out of cards in their deck and need to draw one
The deck is either going to be marginally nerfed or completely nuked later today, and neither situation is great for anyone who has a bunch of those staples kicking around