Deadly Cover-Up provides you with a sweeper as needed against the go wide decks, but also really shines against slower decks to remove their win conditions and important cards
The unconditional and irreplaceable utility of Fierce Guardianship runs against that spirit of innovation, presenting players with all-purpose power they can no longer justify skipping over
Sure, winning the game consistently by turn four is fun, but wheres the variety, the spice
FalCie Paradise You cant main deck this, but wow would getting hosed by this feel absolutely miserable
Ovinomancer (Mirage/Visions/Weatherlight) Black and Red might get reusable creature kill, but those usually are the only two cards to have this resource
Thats seriously formidable power, before you even start challenging using its huge strength