Serra's Emissary shuts down a full board of any-sized creatures while also offering a bigger evasive body
Which Deck to build: After the first week of playing and you have unlocked all the standard and you are either a veteran looking for what to play or you are by now a more experienced beginner and looking for the first deck to build and start grinding
Many cards from each of the sets have also become hugely sought after among collectors, with the latest set, Ursulas Return, being no different in that regard
Even without those ramp effects, this costs just one more mana than Teferi himself, and its going to draw a ton of cards very quickly
The three mana isnt so curve-friendly, but you can deal damage to any target, you can proliferate, and it's an instant
The Legality of it All Perhaps most importantly, abolishing the reserved list would probably lead to a lot of legal cases against WotC