Id lead with Emerald and Strip Mine in to Sylvan Library on the first turn
When deposit and withdrawal steps are laid out plainly, users can focus on the excitement of reels, cards, and live tables rather than wrestling with technicalities
Typically the kinds of deck that want coverall counterspells also want to leave mana up to be reactive, having to tap five mana in your upkeep will make the turns following a Pact of Negation deeply uncomfortable until you have lots and lots of mana
You have to cast your spells precombat, which you dont always want to do, and on top of that, you need both a creature and noncreature
There are a bunch of different ways to abuse the card alongside Landfall triggers and sacrifice outlets, so it makes for a reliable alternate win condition in decks like Aristocrats
That's 2 damage to their combined 30 life