Caesar freely confessed to me that the greatest actions of his own life were not equal, by many degrees, to the glory of taking it away. I had the honor to have much conversation with Brutus; and was told that his ancestor Junius, Socrates, Epaminondas, Cato the Younger, Sir Thomas More, and himself, were perpetually together: a sextumvirate to which all the ages of the world cannot add a seventh.

What would be the best suggestion to give to Jonathan Swift for improving the allusion in the passage?

Provide some explanation of what made Junius, Socrates, Epaminondas, Cato the Younger, and Sir Thomas More such an interesting group.
Give the time and place of the events.
Add to the middle of the passage one long sentence full of imagery and figurative language.
Invent three fake philosophers with unusual names and include them in the passage.

The answer is A: Provide some explanation of what made Junius, Socrates, Epaminondas, Cato the Younger, and Sir Thomas More such an interesting group.

Although lacking in modesty, one could recommend the answer above to the great satirist writer, Jonathan Swift, to improve the allusion in the passage. Being a learned man, Swift had control over the thoughts of the characters cited, but, then, as now, it would have been illuminating for the common reader to expand on the thoughts that made each character relevant and why they´d be put into a single group, they who were, in so many ways, so different: Junius, the Stoic philosopher, Socrates, the lover of wisdom, Epaminondas and Cato the younger, the wise Greek and Roman statesmen, respectively, and, finally, More, English philosopher and statesman alike.