To expand upon the above analysis a little before jumping into the next one: Let's start with Aether Vial. A world where mana denial is less powerful than maybe any other point in the format's history (at least since I started playing in 2013). A world where Thalia, Guardian of Thraben is arguably not even the best 2 drop hatebear in the deck (sorry Thalia, Guardian of Thraben, Spirit of the Labyrinth is busted). We live in a world where the fair decks have more answers for Aether Vial, the combo decks care even less about your Aether Vial, and D&T itself needs Aether Vial less. In Death & Taxes, this argument takes the form of “You always want to draw Aether Vial, Thalia, Guardian of Thraben, Wasteland, Rishadan Port, etc.” In the world of 2020 Legacy, however, this argument does not bear nearly as much weight as it did in the past. Powerful cards have fairly unique identities. that you don't have similarly powerful cards to fill out the 61st+ card(s) in your deck.the power level curve of your deck is fairly high (IE: your 1st best card is waaaaaay better than your 30th best card).The crux of this argument hinges on the idea that for the most part, your best cards are much better than whatever the “next best” cards you could use to replace them, and decks are fundamentally designed to want to draw and use their best cards.
The problem with this is that it doesn't fully address the situation, especially when you add Yorion, Sky Nomad into the math. It's been the strongest argument for not playing > 60 cards in your deck since… basically forever. Let's start with the elephant in the room: “You draw your best cards less often.” This is the exact argument I hear time and time again when it comes to Yorion, Sky Nomad. In lieu of fighting the exact same argument over and over again, I wanted to put all of my thoughts in one place so people could hear exactly what I had to say on the topic. Since the advent of Yorion D&T about a month ago, there has been a decent amount of pushback from some of the community, either doubting the strength of Yorion, Sky Nomad or valuing the consistency of a 60 card deck.