As mentioned above, the Malbim and the Vilna Gaon explain that Haman’s confusion stemmed from the fact that he was in the presence of both the king and queen, so he could not use either of his excuses.
Similarly, according to the Maharal, Achashverosh asked Esther why she invited Haman to the party if he is so evil. She answered that she did so intentionally to avoid the possibility of Haman giving excuses if he were confronted without both of them present.
The verse has a combined gematria of 3355, the same as the verse (Bireishis 38:17) regarding the amount of money Yehudah pledges to Tamar. It also has the same gematria as the verse (Devarim 13:10) commanding the punishment for someone who encourages others to worship idol. Finally, it also has the same gematria as the verse in Tehillim (67:4) that the nations are happy when H-Shem governs the nations. Perhaps, just as the verse climactically demonstrates H-Shem’s active rescue of the Jews from their impending holocaust, all of these verses have to do with H-Shem’s supervision of the world. Just as the Talmud (Sotah 10a) says that He was involved with the otherwise seemingly elicit relationship between Yehuda and Tamar, so too He alone should be worshiped – without the false gods of idolatry. Similarly, the point of our world is to reach the level where everyone recognizes the guiding Hand of H-Shem in all of the events of the world.