The choice between Esper and Jeskai in Modern has always favored the latter because of Lightning Bolt. It’s perhaps the single best card in Modern, and no other one-mana removal spell is as effective. So at first glance the swap to Disfigure in this Esper list appears to doom the list from the get-go.
But if you look at the Modern format right now, there aren’t a lot of three-toughness creatures. Wild Nacatl has fallen off from the spring, and some Burn lists are cutting it. You still lose out on the ability to go upstairs and gain some reach, which is important against the various combo decks in Modern, so you need to recoup that with hard-hitting threats.
Tasigur, the Golden Fang; Gurmag Angler; and Geist of Saint Traft certainly fill that role nicely. All come down on the first few turns and threaten to end the game very quickly. That dynamic really changes this deck by making it significantly more aggressive. There are no counterspells here to leave up mana; every card can be played proactively.
But the Lingering Souls and planeswalkers give the deck a second angle. They can all pressure the opponent or clear the way for your other threats, but they add a necessary element of resilience against decks like Jund, Abzan, and Jeskai. As much as it is en vogue to bemoan Modern as non-interactive and lightning-fast, you still have to prepare for the ubiquitous midrange decks of the format. They never go away, and if you ignore them, they will not be forgiving.
Jace, Vryn’s Prodigy fits this deck better than Snapcaster Mage, since you lack the reactive elements that make flash attractive. Notably, Jace can clear a blocker for your Geist of Saint Traft with its +1 rather than flashing back a spell.
Last, the switch from Serum Visions to Thought Scour may seem odd at first, but Thought Scour really ties the room together. It feeds Jace, Vryn’s Prodigy and delve; mills Lingering Souls for value; and, like Serum Visions, gives you a card you can Flashback for value regardless of the situation.
When people think of Esper, they typically think control. But sometimes that mindset can be deceiving, especially with a format like Modern that has such a diverse array of powerful threats. Eschewing Snapcaster Mage sounds strange but makes sense in a deck like this, as does cutting all the counterspells. It’s important not to get caught up in sacred cows and instead build each deck as a separate entity. A deck is more than a collection of cards, and this deck is certainly an example of that.