The Diad seem pretty much unkillable, shrugging off even the biggest guns. How can apparently unkillable energy beings eventually be defeated? By several agents taking a page from Ghostbusters and crossing the streams at them (even though High T claims it was just a matter of getting the proper voltage.)
Retcons apart in regards to when and where the MiB came to be, the revelation that Gustave Eiffel was a founding member is brilliant when one remembers that he designed not only the tower that bears his name, but was also involved in the creation of the Statue of Liberty. Which, as anyone who's watched Men in Black II ought to know, is actually a giant Neuralyzer.
Oddly, Agent H often acts like a goofball instead of the competent agent he is supposed to be. When Agent H was neuralyzed, High T/the Hive likely eliminated quite a bit more than just the events of the Hive's "defeat" - both to ensure an agent known to be competent couldn't thwart the Hive's plans in the future, and because H might otherwise notice there was something odd about the behaviour of his mentor/father figure. Also doubles as Fridge Brilliance.