That's also a great point. With traditional intelligence, it's unthinkable to sail your army far away to land right next to the enemy capital unless you vastly overpower your enemy anyways. With spying, you know where to land without a loss and when to do so to prevent the enemy from being able to retaliate, offering the deadly possibility of landing safely and rushing to the enemy capital before they can react. You can often then even start a takeover of their capital...
I'd grant that spying is more lucrative in the current naval game. The enormous variety of potential destinations and the huge power asymmetry that manifests upon landing versus an amphibious assault lend themselves towards empowering espionage. Naval landings seem only likely to succeed against essentially undefended shorelines, which means they have to be surprise attacks.
So countries with disproportionately maritime borders (D'Hara) may be uniquely susceptible to espionage, and may also stand to benefit more from it.
