The Magic: The Gathering sets available on Arena only include ones from its release onward, so you cant play super old decks from a decade ago
While this may be a small change, the color of cards is obviously hugely important in MTG, even with Fetch Lands versatility
The deck then adds a ton of different wrath effects (Star of Extinction, Razia, Austere Command, Blasphemous Act, Day of Judgment, etc) to deal with any threats your opponents might be able to cast prior to you repeatedly wiping the board of lands
The best systems allow point redemption at predictable rates and offer seasonal perks that keep engagement fresh
This lets you slam down the Herald seconds before certain doom, giving you a chance to cast it in response to practically anything your opponent could do
Caging Aetherling lets Mairsil blink on demand, along with additional abilities to use once each turn